SIGMA Ransomware

What is SIGMA?

SIGMA is a ransomware-type virus discovered by malware security researcher, Michael Gillespie. This high-risk malware is distributed using spam emails that contain a message stating that users will be charged $3000+ from their MasterCard, unless they open a MS Office document attached.

After opening this attachment and entering the password provided, users will inadvertently execute configured macros, which will then immediately perform a number of actions to download and run SIGMA ransomware.

Once infiltrated, this virus encrypts stored data using RSA-2048 cryptography and appends four random letters/digits to the name of each encrypted file (e.g., "sample.jpg" might be renamed to a filename such as "sample.jpg.Ka8E"). Immediately after encryption, SIGMA changes the desktop wallpaper and places two files ("ReadMe.html" and "ReadMe.txt") on the desktop.

The new desktop wallpaper contains a short message encouraging victims to read the new HTML/.txt files, which will provide detailed information regarding the current situation and what to do next. The HTML and .txt files contain identical content - stating that stored files are encrypted and can only be restored using a unique decryption key, together with a special tool.

Unfortunately, this information is accurate. As mentioned above, SIGMA uses the RSA-2048 encryption algorithm, which generates public (encryption) and private (decryption) keys. Since restoring files without the private key is impossible, criminals hide it on a remote server and demand a ransom to receive it.

The cost of the decryption key and associated tool is $1000 in Bitcoins, however, the message also states that the cost will double after seven days. To submit payment, users are encouraged to visit SIGMA's Tor website and follow instructions provided. Note is that users can use a XAMP live chat to contact cyber criminals.

They are also permitted to send several files to SIGMA's developers. The criminals then decrypt these files and return them as a 'guarantee' that decryption is possible. Bear in mind, however, that cyber criminals cannot be trusted. These people often ignore victims, once payments are submitted.

There is no guarantee that your files will ever be restored and you will probably be scammed. Paying will simply support cyber criminals' malicious businesses and you will receive nothing in return. Therefore, we strongly advise you to ignore all requests to contact these people or pay ransoms.

Unfortunately, there are no tools capable of cracking RSA-2048 cryptography and restoring files compromised by SIGMA. The only option is to restore files/system from a backup.

Screenshot of a message encouraging users to pay a ransom to decrypt their compromised data:

There are dozens of ransomware-type viruses virtually identical to SIGMA. For example, Powerful Hidden Tear, Relock, Teamo, GIBON, and many others. Although these viruses are developed by different cyber criminals, their behavior is identical. All encrypt data and make ransom demands.

Research shows that the only major differences are type of encryption algorithm used and size of ransom.

Unfortunately, most of these viruses employ algorithms that generate unique decryption keys (e.g., RSA, AES, etc.) Therefore, unless the malware contains bugs/flaws (e.g., the key is hard-coded or stored locally), restoring files manually without involvement of developers (contacting these people is not recommended) is impossible.

SIGMA and other ransomware-type viruses present a strong case from maintaining regular data backups. Bear in mind, however, that backup files should be stored on a remote server (e.g., Cloud) or an unplugged hard drive, otherwise they will also be encrypted.

How did ransomware infect my computer?

As mentioned above, SIGMA is proliferated using spam emails, however, to spread other ransomware-type viruses, developers often employ trojans, fake software update tools, peer-to-peer (P2P) networks, and other third party download sources. Trojans open "backdoors" for viruses to infiltrate the system.

Fake software updaters install viruses by misusing outdated software bugs/flaws. P2P networks (torrents, eMule, etc.) and other unofficial software distribution sources (freeware download websites, free file hosting websites, etc.) often present malicious executables as legitimate software, thereby tricking users into downloading and running malware. Essentially, the main reasons for computer infections are poor knowledge and careless behavior.

How to protect yourself from ransomware infections?

The key to computer safety is caution. Therefore, pay close attention when browsing the Internet. Never open attachments received from suspicious email addresses - these emails should be deleted without reading.

We also strongly recommend that you download your software from official sources only and, preferably, using a direct download link (third party download/installation tools often include dubious apps).

Furthermore, keep installed software updated and use a legitimate anti-virus/anti-spyware suite, however, it is important to note that ransomware is proliferated using fake updaters. Therefore, software should never be updated using unofficial tools.

SIGMA ransomware is being distributed using email messages with infected attachments. Here's a sample of an email message that distributes this ransomware:

Text presented in this rogue email:

Hey there! I hope you are well!
I am definitely interested in a opening.
See my attached CV and get back to me as soon as possible!
The file is password protected to protect against identity theft. The password is "resume".
Looking forward to hearing back from you!
Meriwether

Cyber criminals have attached a malicious .doc file to this email message, if a user launches this file and enables macros, his/her computer will be infected with SIGMA ransomware:

Screenshot of SIGMA HTML file:

Text presented within SIGMA ransomware HTML and .txt files:

What has happened to my files ? Why i am seeing this ?

All of your files have been encrypted with RSA 2048 Encryption. Which means, you wont be able to open them or view them properly. It does NOT mean they are damaged.

Solution

Well its quite simple only we can decrypt your files because we hold your RSA 2048 private key. So you need to buy the special decryption software and your RSA private key from us if you ever want your files back. Once payment is made, you will be given a decrypter along with your private key , once you run that , All of your files will be unlocked and back to normal.


So there are 2 ways to do this either you wait for a miracle and get your price doubled or follow instructions below carefully and get back your all important files.

Payment procedure

Download a special browser called "TOR browser" and then open the given below link. Steps for the same are -

1. Go to hxxps://www.torproject.org/download/download-easy.html.en to download the "TOR Browser".
2. Click the purple button which says "Download TOR Browser"
3. Run the downloaded file, and install it.
4. Once installation is completed, run the TOR browser by clicking the icon on Desktop.
5. Now click "Connect button", wait a few seconds, and the TOR browser will open.
6. Copy and paste the below link in the address bar of the TOR browser.


hxxp://yowl2ugopitfzzwb.onion/

Now HIT "Enter"

7. Wait a few seconds, and site will open then enter your GUID mentioned below and process.

303FE8580B3167E7E1141B8AAE588AA2

If you have problems during installation or use of Tor Browser, please, visit Youtube and search for "Install Tor Browser Windows" and you will find a lot of videos.

Screenshot of SIGMA desktop wallpaper:

Screenshots of SIGMA website:

Home:

Text presented within this page:

Sigma Ransomware

Your documents, photos, databases and other important files have been encrypted
Your files were encrypted at Nov 7 2017 7:05 AM
To recover them you need the private key of the key pair used to encrypt them and the decryptor software.
You can buy both of them for $1000.00
Within 7 days you can purchase this product at a special price: ˜ $1000
After 7 days the price of this product will increase up to: ˜ $2000
Final deadline is 06-01-2018 03:05:01 (after that you will loose your important files forever)
Register a bitcoin wallet.
Create a Bitcoin Wallet (we recommend Blockchain.info) or other wallets (click here)
Purchase the required amount of bitcoins.
There are several ways you can buy bitcoins, you can use bitcoin exchanges (click here), buy directly from people selling near you (click here) or using a bitcoin ATM (click here)
Send exactly $1000.00 to the address:
1FTgiZwhTJ1HY4gmvieio88UAfBxQtVDNj The confirmation may take several minutes, please be patient.
Status: payment awaiting...
This payment request is valid until 14-11-2017 03:05:01 UTC after that it will get double ˜ $2000
In case of any problems with payment or having any other questions, please contact us via LIVE CHAT

Live Chat:

Text presented within this page:

FOR CONNECT WITH US All YOU NEED IS ONE XAMP ACCOUNT , PIDGIN WITH OTR FOR SECURE INSTANT MESSAGING
Pidgin Installation Guide hxxps://securityinabox.org/en/guide/pidgin/windows/
Some secure and fast XAMP sites we recommend
exploit.im (registration can be done within pidgin)
hxxps://accounts.jwchat.org/
hxxps://jabb.im/reg/
After you done with installing Pidgin and OTR (its very important to install OTR so please dont forget it) add our XAMP as buddy and authorised it
Not only that when we chat with you in pidgin we can decrypt 1 file for free for you or may be more..
Our XAMP Account is Sigmaxxx@jabb.im

FAQ (Frequently Asked Question):

Text presented within this page:

Question: How can i decrypt my files after payment?
Answer: After payment, you can download the from your personal page. We guarantee that all your files will be decrypted!

Question: My files was infected more then month ago, can i still decrypt it with your software?
Answer: Yes, you can still decrypt your files after the payment we keep your keypair for 2 months then its gets delte automatically and its impossible to recover your files after that!

Question: I do have multiple computers infected is there any discount?
Answer: Please follow instructions mentioned on live chat page and connect with us we can negotiate for multiple computers

Question: So if i pay and get my files back am i secure in future from this ransomware ?

Answer: we sale special Immunity as low as 100$ more on top of the decrypter payment if you buy it , we add your machine GUID to our whitelist and in future your machine never ever get infected again for buying immunity please follow instructions mentioned on live chat page and connect with us !

Screenshot of files encrypted by SIGMA (extension of 4 random letters and digits):

SIGMA ransomware removal:

Instant automatic malware removal:

Manual threat removal might be a lengthy and complicated process that requires advanced IT skills. Combo Cleaner is a professional automatic malware removal tool that is recommended to get rid of malware. Download it by clicking the button below:

By downloading any software listed on this website you agree to our Privacy Policy and Terms of Use. To use full-featured product, you have to purchase a license for Combo Cleaner. 7 days free trial available. Combo Cleaner is owned and operated by RCS LT, the parent company of PCRisk.com.

Removal and file recovery procedure

If your files are encrypted with a new extension and a ransom note has appeared, you've been hit by ransomware. Don't pay. The procedure below works in order: contain the infection, identify the variant, remove the ransomware itself (so anything you restore doesn't get re-encrypted), and try to recover files using free decryption tools, Windows Volume Shadow Copies, or backups. Run a full system scan with Combo Cleaner to remove the infection - then move on to file recovery.

Common ransomware behaviors

VisibleEncrypts your files and renames them

The ransomware reads each file, encrypts the contents with the attacker's public key, and writes the encrypted bytes back to disk. Most variants also rename the file by appending a new extension - .net, .locked, .crypt, .lockbit, .djvu, etc. Without the matching private key, the encrypted files cannot be opened normally. Recovery depends on a free decryption tool, a recoverable Volume Shadow Copy, or a clean backup.

VisibleDrops a ransom note in every encrypted folder

A text or HTML file (usually named HOW_TO_DECRYPT.txt, README.txt, _readme.txt, or similar) is placed in every folder that contains encrypted files. The note explains the situation, lists a payment amount in cryptocurrency, gives a deadline, and provides a contact email or .onion site. Save the note - don't delete it. Its exact wording, the email address, and the bitcoin wallet are how you identify the variant in the next phase.

VisibleReplaces the desktop wallpaper

Many ransomware variants change the Windows wallpaper to a black or red image with the ransom message and instructions. The wallpaper is just a visual scare tactic - it doesn't add any actual capability and reverts to normal once the ransomware is removed. Photograph it before removal in case the contact details are useful for variant identification or for reporting to authorities.

HiddenDeletes Volume Shadow Copies

One of the first things modern ransomware does after launching is run vssadmin delete shadows /all /quiet to wipe Windows' built-in Volume Shadow Copies - the snapshots that Previous Versions and System Restore rely on. Some ransomware doesn't fully succeed (especially on systems where the user lacks full admin rights), leaving partial shadow copies recoverable. Phase 4 step 11 covers how to check what survived.

HiddenDisables Windows Defender and other security tools

Before encrypting, the ransomware tries to silence anything that could alert you or block it - Windows Defender real-time protection, third-party antivirus services, backup agents (Veeam, Acronis), and sometimes the Windows Event Log service. It often modifies Group Policy or registry keys to keep these off after reboot. Phase 3 step 9 explicitly turns Tamper Protection back on so the next ransomware attempt can't repeat the trick.

HiddenSpreads laterally to other PCs on the network

Network-aware ransomware (LockBit, Conti, BlackCat, Akira families) doesn't stop at the first machine. It scans for SMB shares, mapped drives, and other PCs on the same network, then encrypts whatever it can reach. On Windows domains, a single compromised user with admin rights can lead to all-domain encryption. This is why Phase 1 step 2 disconnects the network as the very first action - it stops the spread immediately.

HiddenSteals data before encrypting (double extortion)

Modern ransomware (LockBit, BlackCat / ALPHV, Akira, Cl0p, Royal) almost always exfiltrates data before encrypting. The attacker then runs a "double extortion" play: pay the ransom for decryption, plus pay again to prevent the stolen data from being leaked on the group's leak site. Paying the first ransom does not get the leaked data back - assume that anything the ransomware could read was uploaded. This is one more reason not to pay: the data is already out.

Tools you'll need

Combo Cleaner Antivirus 7-days free trial

Recommended primary scanner. VB100 certified. Removes the ransomware infection so file recovery doesn't get re-encrypted.

Microsoft Defender Offline Free · built-in

Built into Windows. Scans before Windows fully loads to catch persistence the running scanners miss.

Microsoft Safety Scanner (MSERT) Free

Microsoft's free on-demand scanner. Always-current signatures - the binary expires every 10 days.

ID Ransomware Free · web

Upload a ransom note and a sample encrypted file - identifies the variant family and tells you whether a free decryptor exists.

No More Ransom Project Free · web

Joint project of Europol, Dutch Police, and security vendors. Free decryption tools indexed by ransomware family.

Shadow Explorer Free

Browse Windows Volume Shadow Copies as a normal file tree - useful when ransomware partially failed to delete them.

Recuva Free

Deleted-file recovery. Long-shot for ransomware - only helps if the variant deleted unencrypted originals before encrypting copies.

Phase 1~ 5 min

Don't pay & contain

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1

Don't pay the ransom

1 min · read⚠ Do not skip

Paying the ransom does not guarantee you'll get your files back. Major ransomware response studies consistently show that a meaningful percentage of paying victims either receive a non-working decryptor, only partial decryption, or no decryptor at all. Beyond that:

• Paying confirms you as a willing target - re-attack rates within 12 months are high
• Several ransomware groups have been sanctioned (US OFAC, UK OFSI). Paying these groups may be illegal under sanctions law in your country
• The ransom funds the next attack - on you or someone else
• Modern ransomware almost always exfiltrates data first, so paying doesn't get the leaked data back. Assume anything the malware could read was uploaded
• Decryptors, even when they work, often leave files corrupted because the encryption itself was buggy or rushed

The path below tries every legal, free recovery option first. Pay only as an absolute last resort, after consulting a lawyer and your country's cyber crime authority.

2

Disconnect from the network and log out of cloud storage

2 minNo tool needed

Pull the Ethernet cable and turn off Wi-Fi on the affected PC. If multiple computers share the network, do the same on every machine you suspect could be affected, including any servers and NAS units.

Then sign out of cloud storage clients (OneDrive, Dropbox, Google Drive, iCloud) from their app settings. If you can, pause the sync. Some ransomware uses the running sync client to push encrypted versions over your clean cloud copies.

Why this matters

Modern ransomware spreads laterally across SMB shares, mapped drives, RDP, and reachable network neighbors. Disconnecting stops the spread the moment you do it. Logging out of cloud sync clients prevents the ransomware from encrypting the cloud copies of your files via the sync API.

3

Unplug external drives and USB storage

1 minNo tool needed

Safely eject any external drives, USB sticks, SD cards, and network-attached storage shares - then unplug them. If a drive was connected when the ransomware ran, the files on it may already be encrypted, but unplugging stops further damage.

Critically: don't reconnect any drive (including your most recent backup) to this PC until the ransomware is removed in Phase 3. Reconnecting an external backup to an actively-infected PC is the most common way that backup gets encrypted too.

Phase 2~ 5 min

Identify the variant

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4

Save the ransom note and a sample encrypted file

2 min

Copy the ransom note and one small encrypted file (under 1 MB) to a USB stick, or photograph the note with your phone. You'll need both for the variant identification step.

The ransom note is usually one of:

• A .txt file in every encrypted folder (typically HOW_TO_DECRYPT.txt, README.txt, or _readme.txt)
• An .html file with the same purpose
• A changed desktop wallpaper - photograph it
• A lock-screen interrupt that runs at startup - rarer

Important

Don't delete the note. Variant identification depends on its exact wording, the contact email, and the bitcoin wallet address. The note is also evidence if you report to authorities.

5

Identify the variant with ID Ransomware

Tool: ID Ransomware3 min

From a clean device (your phone is fine, or another PC that wasn't on the affected network), visit id-ransomware.malwarehunterteam.com. Upload the ransom note and the sample encrypted file. The site identifies the variant family and tells you whether a free decryptor exists.

Pro tip

ID Ransomware is run by the Malware Hunter Team. Files you upload are kept private - they're used for analysis, not published. If you're concerned about uploading data anyway, you can paste the contact email and bitcoin wallet from the note - those are often enough for identification.

Phase 3~ 30-45 min

Remove the ransomware

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The ransomware itself must be removed before any file recovery. If it's still active, anything you restore in Phase 4 gets re-encrypted within minutes.

6

Boot to Safe Mode with Networking and download the scanners

5 min

Safe Mode loads only the minimal Windows drivers, which prevents most ransomware from auto-running while you set up the scanners.

Windows 11: open Settings → System → Recovery, click Restart now next to Advanced startup. After the restart, click Troubleshoot → Advanced options → Startup Settings → Restart, then press 5 or F5.

Windows 10: click the Windows logo, hold Shift, click the Power icon and choose Restart. From the Choose-an-option screen, click Troubleshoot → Advanced options → Startup Settings → Restart, then press F5.

Once Safe Mode has loaded, turn Wi-Fi back on and download Combo Cleaner (used in step 8) and Microsoft Safety Scanner (used in step 9). Save both installers to your Desktop, then disconnect Wi-Fi again before scanning.

7

Run Microsoft Defender Offline

Tool: Built into Windows15 min

Reboot to normal Windows. Open Windows Security → Virus & threat protection → Scan options. Select Microsoft Defender Antivirus (offline scan) and click Scan now. The PC restarts into a stripped-down environment and scans the disk before Windows fully loads.

Why this comes first

Some ransomware variants drop bootkit components or kernel hooks that hide from any scanner running on the same Windows session that's already infected. A pre-boot offline scan sees the disk before the malware can load itself.

Recommended antivirus

Combo Cleaner

VB100 certified. Includes anti-trojan, registry/persistence scanning, and anti-spyware in one pass. The 7-day free trial is available.

Download Combo Cleaner

8

Run a full Combo Cleaner scan

Tool: Combo Cleaner20-40 min

Run the installer you downloaded in step 6 and start a full system scan (not the quick scan). Let it complete, review what it detected, and apply the recommended actions. Combo Cleaner quarantines the ransomware executable and the registry / scheduled-task entries that re-launch it on reboot.

9

Run Microsoft Safety Scanner and re-enable Defender

Tool: MSERT15 min

Run Microsoft Safety Scanner (MSERT.exe) as a second-opinion full scan. The binary expires every 10 days so the copy you downloaded has the latest signatures.

Once it finishes, open Windows Security → Virus & threat protection → Manage settings and confirm Real-time protection, Cloud-delivered protection, and Tamper Protection are all on. Many ransomware variants disable Defender during the attack - this is where you switch it back on so the next attempt can't repeat the trick.

Why a second scan

Different scanning engines catch different threats. Running an additional Microsoft scan after Combo Cleaner is the most underused verification step in malware removal - and free.

Phase 4~ 30-60 min · results vary

Try to recover files

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Try the steps in order. The first decryptor that works ends the recovery process - no need to do all four.

10

Check the No More Ransom Project for a free decryptor

Tool: nomoreransom.org★ Cleanest path if listed5 min

Visit nomoreransom.org and search the Decryption Tools list for the variant name returned by ID Ransomware. The project is run by Europol, the Dutch Police, and security vendors - everything listed is legitimate and free.

If a decryptor exists, download it onto a clean PC, copy it across, and follow its instructions exactly. Decryptors usually want you to point them at a sample encrypted file plus its known unencrypted version (sometimes any image you previously had a backup of works).

Free decryptors exist for parts of the STOP/Djvu, GandCrab, REvil, Avaddon, Conti and Hive families, among others. Most modern variants don't have public decryptors - if yours isn't listed, that's expected; move to the next step.

11

Try Windows Volume Shadow Copies

Tool: Shadow Explorer / vssadmin15 min

Windows automatically creates Volume Shadow Copies of files when System Restore points are made or scheduled backups run. Most ransomware tries to wipe these (vssadmin delete shadows /all /quiet), but the deletion sometimes fails partially - especially if the running user doesn't have full admin rights. When it does fail, snapshots survive that contain pre-encryption versions of your files.

First, check what's there. Open Command Prompt as Administrator and run:

vssadmin list shadows

If you see entries listed, shadow copies survived. To restore from them:

• Built-in: right-click any folder → Properties → Previous Versions tab. Pick a snapshot dated before the infection and restore.
• Better tool for browsing: install Shadow Explorer (free). It shows all snapshots as a normal file tree and lets you copy out only the files you want.

Why check this even when there's a decryptor

Shadow Copies recover the original files exactly, with no risk of decryption errors. If they survived, this is faster and cleaner than running a decryptor on the encrypted set.

12

Restore from cloud or external backup

Tool: your backup software30 min

If you have a backup that pre-dates the infection, this is the cleanest recovery available. Important precautions:

• Don't reconnect a backup drive until Phase 3 is complete. If the ransomware is still active, plugging in the backup encrypts it too.
• For cloud backups (OneDrive, Dropbox, Google Drive, iCloud), use the Version History feature to roll individual files back to pre-encryption versions.
• OneDrive specifically has a "Restore your OneDrive" feature: if it detected mass file changes, you can roll back the entire account up to 30 days. Sign in at OneDrive on the web, click the Settings gear, and choose Restore your OneDrive. Microsoft 365 subscribers also get ransomware detection alerts; non-subscribers get one free recovery.
• Verify the restored files open correctly before you delete the encrypted set. Test a few documents, photos, and any database / project files.

13

Try Recuva as a last-resort recovery

Tool: Recuva30 min

Recuva is a long shot, not a primary recovery tool. Most modern ransomware encrypts files in place - it reads the original, encrypts the data, and writes the encrypted bytes back to the same disk location. In that case, the original isn't deleted, just rewritten - and Recuva has nothing to find.

But for older or simpler variants that deleted originals before creating encrypted copies (rather than encrypting in place), Recuva can sometimes pull the originals from unallocated disk space. Worth trying as a last resort, especially before you use the disk much further.

If you try it:

• Stop using the disk as much as possible - every disk write reduces recovery odds
• Run Recuva from a USB stick, not from the affected disk
• Use Deep Scan mode (slower but the only mode worth running for this scenario)

Don't skip the steps above expecting Recuva to bail you out. It works in maybe 5-20% of cases, depending on the variant and how soon you try.

Phase 5~ 20 min + ongoing

Report & prevent re-infection

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14

Report the attack to authorities

10-20 min

Even if your files aren't recovered, your report helps authorities track variants, attribute groups, and warn future victims. In some jurisdictions (especially the US and UK) early reporting can sometimes help recall a wired ransom payment via banking partners.

United States: ic3.gov (FBI) + stopransomware.gov (CISA)

United Kingdom: reportfraud.police.uk (Report Fraud, the successor to Action Fraud) + NCSC

Canada: antifraudcentre.ca

Australia: ReportCyber

Spain: Policía Nacional (Oficina Virtual de Denuncias)

France: cybermalveillance.gouv.fr

Germany: BKA

Italy: Polizia Postale

Netherlands: Politie

Poland: CERT Polska

Portugal: CNCS

EU (other): your national CERT

Save the report number - banks, insurers, and credit bureaus will ask for it. If you operate a business, you may also have legal disclosure obligations (GDPR in the EU, state breach laws in the US) that run on a 72-hour clock.

15

Plan 3-2-1 backups going forward

30 min initial

The single best defense against ransomware is a tested backup. Use the 3-2-1 rule:

• 3 copies of your data
• 2 different storage media (e.g., internal drive + external drive)
• 1 offline / air-gapped copy (an external drive that isn't always connected)

Recommended cadence:

• Daily: cloud sync (OneDrive, Dropbox, Google Drive) - convenient, but vulnerable if the ransomware reaches the sync folder. The Version History feature is what saves you
• Weekly: external drive that you connect briefly, then disconnect - the air-gap is what protects against ransomware
• Monthly: a second external drive stored off-site (different physical location) - protects against fire, theft, flood

Important

Test the backup at least once. Open a few files from it, check sizes match, restore one to a different folder. An untested backup isn't a backup - it's a hope.

16

Patch the entry point and monitor for 30 days

5 min/day · 30 days

Most reinfections happen via the same vector that worked the first time. Until you've patched the entry point, watch for:

• Unusual disk activity, unexpected file modifications, or unfamiliar processes in Task Manager
• Unexpected reboots or new accounts you didn't create
• Defender or your antivirus turning itself off again

Common entry vectors and what to do about each:

• Phishing email with a malicious attachment - review email filters and train yourself / staff to recognise the patterns - see pcrisk's Phishing/Scam reference
• Exposed RDP with weak passwords - disable Remote Desktop from Settings → System → Remote Desktop if you don't need it. If you do, put it behind a VPN and require a long password plus MFA
• Unpatched VPN appliances or public-facing apps - check the vendor's advisories page and apply the latest firmware
• Cracked / pirated software - was the most common vector for STOP/Djvu in particular. Don't run software from torrent sites

Run a Combo Cleaner scan weekly for the first month. Update Windows, browsers, and applications aggressively.

Important: Removing a ransomware infection requires a full system scan, not a manual file delete. If you're not confident with the manual procedure, run an automated scan with Combo Cleaner and Windows Defender and stop there - that combination removes the vast majority of consumer ransomware variants. Then move to Phase 4 for file recovery, or to Phase 5 if your files are unrecoverable and you need to start fresh from a clean Windows install.