SIGMA Ransomware

Also Known As: SIGMA virus
Distribution: Low
Damage level: Severe

SIGMA ransomware removal instructions

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:

SIGMA decrypt instructions

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.

Threat Summary:
NameSIGMA virus
Threat TypeRansomware, Crypto Virus, Files locker
SymptomsCan't open files stored on your computer, previously functional files now have a different extension, for example my.docx.locked. A ransom demanding message is displayed on your desktop. Cyber criminals are asking to pay a ransom (usually in bitcoins) to unlock your files.
Distribution methodsInfected email attachments (macros), torrent websites, malicious ads.
DamageAll 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.

To eliminate SIGMA virus our malware researchers recommend scanning your computer with Spyhunter.
▼ Download Spyhunter
Free scanner checks if your computer is infected. To remove malware, you have to purchase the full version of Spyhunter.

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:

sigma ransomware distributing email

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!

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:

sigma ransomware distributing malicious .doc file enable macro

Screenshot of SIGMA HTML file:

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.


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:// 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.


Now HIT "Enter"

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


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:

SIGMA wallpaper

Screenshots of SIGMA website:


SIGMA website

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 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:

SIGMA Ransomware Live Chat

Text presented within this page:

Pidgin Installation Guide hxxps://
Some secure and fast XAMP sites we recommend (registration can be done within pidgin)
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

FAQ (Frequently Asked Question):

SIGMA Ransomware frequently asked questions FAQ

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):

Files encrypted by SIGMA

SIGMA ransomware removal:

Instant automatic removal of SIGMA virus: Manual threat removal might be a lengthy and complicated process that requires advanced computer skills. Spyhunter is a professional automatic malware removal tool that is recommended to get rid of SIGMA virus. Download it by clicking the button below:
▼ DOWNLOAD Spyhunter By downloading any software listed on this website you agree to our Privacy Policy and Terms of Use. Free scanner checks if your computer is infected. To remove malware, you have to purchase the full version of Spyhunter.

Quick menu:

Step 1

Windows XP and Windows 7 users: Start your computer in Safe Mode. Click Start, click Shut Down, click Restart, click OK. During your computer start process, press the F8 key on your keyboard multiple times until you see the Windows Advanced Option menu, and then select Safe Mode with Networking from the list.

Safe Mode with Networking

Video showing how to start Windows 7 in "Safe Mode with Networking":

Windows 8 users: Start Windows 8 is Safe Mode with Networking - Go to Windows 8 Start Screen, type Advanced, in the search results select Settings. Click Advanced startup options, in the opened "General PC Settings" window, select Advanced startup. Click the "Restart now" button. Your computer will now restart into the "Advanced Startup options menu". Click the "Troubleshoot" button, and then click the "Advanced options" button. In the advanced option screen, click "Startup settings". Click the "Restart" button. Your PC will restart into the Startup Settings screen. Press F5 to boot in Safe Mode with Networking.

Windows 8 Safe Mode with networking

Video showing how to start Windows 8 in "Safe Mode with Networking":

Windows 10 users: Click the Windows logo and select the Power icon. In the opened menu click "Restart" while holding "Shift" button on your keyboard. In the "choose an option" window click on the "Troubleshoot", next select "Advanced options". In the advanced options menu select "Startup Settings" and click on the "Restart" button. In the following window you should click the "F5" button on your keyboard. This will restart your operating system in safe mode with networking.

windows 10 safe mode with networking

Video showing how to start Windows 10 in "Safe Mode with Networking":

Step 2

Log in to the account infected with the SIGMA virus. Start your Internet browser and download a legitimate anti-spyware program. Update the anti-spyware software and start a full system scan. Remove all entries detected.

If you cannot start your computer in Safe Mode with Networking, try performing a System Restore.

Video showing how to remove ransomware virus using "Safe Mode with Command Prompt" and "System Restore":

1. During your computer start process, press the F8 key on your keyboard multiple times until the Windows Advanced Options menu appears, and then select Safe Mode with Command Prompt from the list and press ENTER.

Boot your computer in Safe Mode with Command Prompt

2. When Command Prompt mode loads, enter the following line: cd restore and press ENTER.

system restore using command prompt type cd restore

3. Next, type this line: rstrui.exe and press ENTER.

system restore using command prompt rstrui.exe

4. In the opened window, click "Next".

restore system files and settings

5. Select one of the available Restore Points and click "Next" (this will restore your computer system to an earlier time and date, prior to the SIGMA ransomware virus infiltrating your PC).

select a restore point

6. In the opened window, click "Yes".

run system restore

7. After restoring your computer to a previous date, download and scan your PC with recommended malware removal software to eliminate any remaining SIGMA ransomware files.

To restore individual files encrypted by this ransomware, try using Windows Previous Versions feature. This method is only effective if the System Restore function was enabled on an infected operating system. Note that some variants of SIGMA are known to remove Shadow Volume Copies of the files, so this method may not work on all computers.

To restore a file, right-click over it, go into Properties, and select the Previous Versions tab. If the relevant file has a Restore Point, select it and click the "Restore" button.

Restoring files encrypted by CryptoDefense

If you cannot start your computer in Safe Mode with Networking (or with Command Prompt), boot your computer using a rescue disk. Some variants of ransomware disable Safe Mode making its removal complicated. For this step, you require access to another computer.

To regain control of the files encrypted by SIGMA, you can also try using a program called Shadow Explorer. More information on how to use this program is available here.

shadow explorer screenshot

To protect your computer from file encryption ransomware such as this, use reputable antivirus and anti-spyware programs. As an extra protection method, you can use programs called HitmanPro.Alert and EasySync CryptoMonitor, which artificially implant group policy objects into the registry to block rogue programs such as SIGMA ransomware.

Note that the Windows 10 Fall Creators Update includes a "Controlled Folder Access" feature that blocks ransomware attempts to encrypt your files. By default, this feature automatically protects files stored in the Documents, Pictures, Videos, Music, Favorites as well as Desktop folders.

Controll Folder Access

Windows 10 users should install this update to protect their data from ransomware attacks. Here is more information on how to get this update and add an additional protection layer from ransomware infections.

HitmanPro.Alert CryptoGuard - detects encryption of files and neutralises any attempts without need for user-intervention:

hitmanproalert ransomware prevention application

Malwarebytes Anti-Ransomware Beta uses advanced proactive technology that monitors ransomware activity and terminates it immediately - before reaching users' files:

malwarebytes anti-ransomware

  • The best way to avoid damage from ransomware infections is to maintain regular up-to-date backups. More information on online backup solutions and data recovery software Here.

Other tools known to remove SIGMA ransomware:

About the author:

Tomas Meskauskas

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 since 2010. Follow me on Twitter and LinkedIn to stay informed about the latest online security threats. Contact Tomas Meskauskas.

PCrisk security portal is brought by a company RCS LT. Joined forces of security researchers help educate computer users about the latest online security threats. More information about the company RCS LT.

Our malware removal guides are free. However, if you want to support us you can send us a donation.

Removal Instructions in other languages
Malware activity

Global virus and spyware activity level today:

Medium threat activity

Increased attack rate of infections detected within the last 24 hours.

QR Code
SIGMA virus QR code
A QR code (Quick Response Code) is a machine-readable code which stores URLs and other information. This code can be read using a camera on a smartphone or a tablet. Scan this QR code to have an easy access removal guide of SIGMA virus on your mobile device.
We Recommend:

Get rid of SIGMA virus today:

▼ REMOVE IT NOW with Spyhunter

Platform: Windows

Editors' Rating for Spyhunter:
Editors ratingOutstanding!

[Back to Top]

Free scanner checks if your computer is infected. To remove malware, you have to purchase the full version of Spyhunter.