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What is Gru ransomware?
Gru ransomware is designed to encrypt files, change the extension of every encrypted file to ".gru" (for example, it renames "1.jpg" to "1.jpg.gru", "2.jpg" to "2.jpg.gru", and so on), and create the "read_it.txt" text file as its ransom note. Like most ransomware variants, Gru blocks access to files and demands a ransom payment to decrypt them.
Gru ransomware in detail
As stated in the "read_it.txt" (Gru's ransom note), this ransomware encrypts all files, and it is impossible to restore access to them without the help of cybercriminals behind the attack. Victims are informed that they cannot decrypt files without the decryption software that costs $1,500.
It is also stated a ransom has to be paid in Bitcoins. Victims have to send $1,500 in Bitcoins to the provided BTC wallet address. Typically, cybercriminals behind ransomware attacks are the only ones who have the right decryption tools. Therefore, ransomware victims cannot decrypt their files without losing money.
There is no third-party tool that could decrypt files encrypted by Gru, which means victims can restore files for free only if they have them backed up. It is highly advisable not to pay cybercriminals a ransom - it is quite common that victims who pay it get scammed (they do not get any decryption tool even if they pay for it).
Additionally, it is strongly recommended to uninstall ransomware from the compromised machine as soon as possible - it is quite common that malware of this type is designed to encrypt new files (if victims store any new files on their computers after the attack) or install itself on other computers connected to the same network.
Screenshot of a message encouraging users to pay a ransom to decrypt their compromised data:
Similarities with other ransomware variants
A couple of examples of other ransomware variants are Pause, HandShake, and L16. As a rule, malware of this type ensures that victims could not access, use their files by encrypting them and generates a ransom note (e.g., a pop-up window, text file) demanding payment for their decryption.
Two major variables usually are the size of a ransom and the cryptographic algorithm (symmetric or asymmetric) that ransomware uses to prevent victims from accessing their data. Unfortunately, it is rarely possible to decrypt files for free. It can be done only when ransomware is not fully developed, or there is a free decryption tool on the Internet.
In most cases, victims can recover files for free only if they have them backed up. For this reason, it is recommended to have a data backup and keep it stored on a remote server like Cloud, or an unplugged storage device so that ransomware could not encrypt it together with other files.
How did ransomware infect my computer?
Usually, ransomware is distributed using emails, trojans, fake software updaters, software cracking tools (or installers for cracked software), or unreliable sources for downloading files, programs. The main purpose of emails that cybercriminals use to deliver malware is to trick recipients into downloading and opening a malicious file.
Typically, those emails contain malicious links or attachments. In most cases, recipients install malware when they open a malicious Microsoft Office, PDF document, archive file like ZIP, RAR (its contents), an executable file (like EXE), JavaScript file. It is important to mention that most malicious emails are disguised as official letters.
Fake software updaters are distributed mainly through deceptive websites. They are disguised as legitimate tools that are supposed to fix, update software. Although, none of them actually fix or update any software. They install some unwanted, malicious software or infect computers through bugs, flaws of installed software that is out of date.
There are different types of trojans. There are trojans that are used to proliferate malware by designing them to install their payload. Once those trojans are installed, they can infect computers with other malware (e.g., ransomware). Usually, trojans are disguised as legitimate programs.
Questionable sources for downloading files, programs are various Peer-to-Peer networks (e.g., torrent clients, eMule), free file hosting, freeware download, unofficial websites, third-party downloaders. Cybercriminals use them to trick users into downloading and opening malicious files. Typically, those files seem to be regular, harmless.
Software cracking tools are supposed to activate, register software without paying for a license key, serial number (which is against the law). However, they often do not function as expected - it is common that cracking tools are bundled with malware (they install malware on computers). The same applies to installers for cracked software.
| Name | Gru virus |
| Threat Type | Ransomware, Crypto Virus, Files locker |
| Encrypted Files Extension | .gru |
| Ransom Demanding Message | read_it.txt |
| Ransom Amount | $1500 in Bitcoins |
| BTC Wallet Address | bc1qw0ll8p9m8uezhqhyd7z459ajrk722yn8c5j4fg |
| Detection Names | Avast (Win32:RansomX-gen [Ransom]), BitDefender (Generic.Ransom.Hiddentear.A.050879D5), ESET-NOD32 (A Variant Of MSIL/Filecoder.AGP), Kaspersky (HEUR:Trojan.MSIL.Fsysna.gen), Microsoft (Ransom:MSIL/ApisCryptor.PAA!MTB), Full List Of Detections (VirusTotal) |
| Symptoms | Cannot open files stored on your computer, previously functional files now have a different extension (for example, my.docx.locked). A ransom demand message is displayed on your desktop. Cyber criminals demand payment of a ransom (usually in bitcoins) to unlock your files. |
| Distribution methods | Infected email attachments (macros), torrent websites, malicious ads. |
| Damage | All files are encrypted and cannot be opened without paying a ransom. Additional password-stealing trojans and malware infections can be installed together with a ransomware infection. |
| Malware Removal (Windows) |
To eliminate possible malware infections, scan your computer with legitimate antivirus software. Our security researchers recommend using Combo Cleaner. Download Combo CleanerTo 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. |
How to protect yourself from ransomware infections?
It is advisable to download files and programs only from official, trustworthy websites and via direct links. Other sources (e.g., third-party downloaders, unofficial pages) can be used to distribute malware. Attachments (or website links) in received emails that are irrelevant should not be opened as well - they are likely to be malicious.
Software should be updated and activated with tools or functions that its official software developers have designed. It is never safe to use third-party, unofficial updaters or activation tools - they often are bundled with malware. Third-party installers can have malware hidden in them too.
Another issue with cracking tools is that it is illegal to use them to activate software (or use cracked software). Additionally, it is recommended to scan the operating system for threats regularly and do it with a reputable antivirus or anti-spyware software. If your computer is already infected with Gru, we recommend running a scan with Combo Cleaner Antivirus for Windows to automatically eliminate this ransomware.
Text presented in Gru ransomware's text file ("read_it"):
HEY !!!
All of your files have been encrypted
Your computer was infected with a ransomware virus. Your files have been encrypted and you won't
be able to decrypt them without our help.What can I do to get my files back?You can buy our special
decryption software, this software will allow you to recover all of your data and remove the
ransomware from your computer.The price for the software is $1,500. Payment can be made in Bitcoin only.
How do I pay, where do I get Bitcoin?
Purchasing Bitcoin varies from country to country, you are best advised to do a quick google search
yourself to find out how to buy Bitcoin.
Many of our customers have reported these sites to be fast and reliable:
Coinmama - hxxps://www.coinmama.com Bitpanda - hxxps://www.bitpanda.comPayment informationAmount: 0.1473766 BTC
Bitcoin Address: bc1qw0ll8p9m8uezhqhyd7z459ajrk722yn8c5j4fg
Screenshot of files encrypted by Gru (".gru" extension):
Gru ransomware removal:
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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.
Don't pay the ransom
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.
Disconnect from the network and log out of cloud storage
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.
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.
Unplug external drives and USB storage
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.
Save the ransom note and a sample encrypted file
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
.txtfile in every encrypted folder (typicallyHOW_TO_DECRYPT.txt,README.txt, or_readme.txt) - An
.htmlfile with the same purpose - A changed desktop wallpaper - photograph it
- A lock-screen interrupt that runs at startup - rarer
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.
Identify the variant with ID Ransomware
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.
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.
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.
Boot to Safe Mode with Networking and download the scanners
Safe Mode loads only the minimal Windows drivers, which prevents most ransomware from auto-running while you set up the scanners.
Windows 11: open , click Restart now next to Advanced startup. After the restart, click , 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 , 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.
Run Microsoft Defender Offline
Reboot to normal Windows. Open . 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.
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.
VB100 certified. Includes anti-trojan, registry/persistence scanning, and anti-spyware in one pass. The 7-day free trial is available.
Download Combo CleanerRun a full Combo Cleaner scan
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.
Run Microsoft Safety Scanner and re-enable Defender
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 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.
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.
Try the steps in order. The first decryptor that works ends the recovery process - no need to do all four.
Check the No More Ransom Project for a free decryptor
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.
Try Windows Volume Shadow Copies
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.
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.
Restore from cloud or external backup
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.
Try Recuva as a last-resort recovery
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.
Report the attack to authorities
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.
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.
Plan 3-2-1 backups going forward
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
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.
Patch the entry point and monitor for 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 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.
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Tomas Meskauskas
Expert security researcher, professional malware analyst
I am passionate about computer security and technology. I have an experience of over 10 years working in various companies related to computer technical issue solving and Internet security. I have been working as an author and editor for pcrisk.com since 2010. Follow me on Twitter and LinkedIn to stay informed about the latest online security threats.
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