SIGMA Ransomware

Also Known As: SIGMA virus
Damage level: Severe

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:
Name SIGMA virus
Threat Type Ransomware, Crypto Virus, Files locker
Symptoms Can'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 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)

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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://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.


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 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:

SIGMA Ransomware Live Chat

Text presented within this page:

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)
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):

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:

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Video suggesting what steps should be taken in case of a ransomware infection:

Quick menu:

Reporting ransomware to authorities:

If you are a victim of a ransomware attack we recommend reporting this incident to authorities. By providing information to law enforcement agencies you will help track cybercrime and potentially assist in the prosecution of the attackers. Here's a list of authorities where you should report a ransomware attack. For the complete list of local cybersecurity centers and information on why you should report ransomware attacks, read this article.

List of local authorities where ransomware attacks should be reported (choose one depending on your residence address):

Isolating the infected device:

Some ransomware-type infections are designed to encrypt files within external storage devices, infect them, and even spread throughout the entire local network. For this reason, it is very important to isolate the infected device (computer) as soon as possible.

Step 1: Disconnect from the internet.

The easiest way to disconnect a computer from the internet is to unplug the Ethernet cable from the motherboard, however, some devices are connected via a wireless network and for some users (especially those who are not particularly tech-savvy), disconnecting cables may seem troublesome. Therefore, you can also disconnect the system manually via Control Panel:

Navigate to the "Control Panel", click the search bar in the upper-right corner of the screen, enter "Network and Sharing Center" and select search result: Disconnecting computer from the Internet (step 1)

Click the "Change adapter settings" option in the upper-left corner of the window: Disconnecting computer from the Internet (step 2)

Right-click on each connection point and select "Disable". Once disabled, the system will no longer be connected to the internet. To re-enable the connection points, simply right-click again and select "Enable". Disconnecting computer from the Internet (step 3)

Step 2: Unplug all storage devices.

As mentioned above, ransomware might encrypt data and infiltrate all storage devices that are connected to the computer. For this reason, all external storage devices (flash drives, portable hard drives, etc.) should be disconnected immediately, however, we strongly advise you to eject each device before disconnecting to prevent data corruption:

Navigate to "My Computer", right-click on each connected device, and select "Eject": Ejecting external storage devices

Step 3: Log-out of cloud storage accounts.

Some ransomware-type might be able to hijack software that handles data stored within "the Cloud". Therefore, the data could be corrupted/encrypted. For this reason, you should log-out of all cloud storage accounts within browsers and other related software. You should also consider temporarily uninstalling the cloud-management software until the infection is completely removed.

Identify the ransomware infection:

To properly handle an infection, one must first identify it. Some ransomware infections use ransom-demand messages as an introduction (see the WALDO ransomware text file below).

Identify ransomware-type infection (step 1)

This, however, is rare. In most cases, ransomware infections deliver more direct messages simply stating that data is encrypted and that victims must pay some sort of ransom. Note that ransomware-type infections typically generate messages with different file names (for example, "_readme.txt", "READ-ME.txt", "DECRYPTION_INSTRUCTIONS.txt", "DECRYPT_FILES.html", etc.). Therefore, using the name of a ransom message may seem like a good way to identify the infection. The problem is that most of these names are generic and some infections use the same names, even though the delivered messages are different and the infections themselves are unrelated. Therefore, using the message filename alone can be ineffective and even lead to permanent data loss (for example, by attempting to decrypt data using tools designed for different ransomware infections, users are likely to end up permanently damaging files and decryption will no longer be possible even with the correct tool).

Another way to identify a ransomware infection is to check the file extension, which is appended to each encrypted file. Ransomware infections are often named by the extensions they append (see files encrypted by Qewe ransomware below).

Identify ransomware-type infection (step 2)

This method is only effective, however, when the appended extension is unique - many ransomware infections append a generic extension (for example, ".encrypted", ".enc", ".crypted", ".locked", etc.). In these cases, identifying ransomware by its appended extension becomes impossible.

One of the easiest and quickest ways to identify a ransomware infection is to use the ID Ransomware website. This service supports most existing ransomware infections. Victims simply upload a ransom message and/or one encrypted file (we advise you to upload both if possible).

Identify ransomware-type infection (step 3)

The ransomware will be identified within seconds and you will be provided with various details, such as the name of the malware family to which the infection belongs, whether it is decryptable, and so on.

Example 1 (Qewe [Stop/Djvu] ransomware):

Identify ransomware-type infection (step 4)

Example 2 (.iso [Phobos] ransomware):

Identify ransomware-type infection (step 5)

If your data happens to be encrypted by ransomware that is not supported by ID Ransomware, you can always try searching the internet by using certain keywords (for example, a ransom message title, file extension, provided contact emails, crypto wallet addresses, etc.).

Search for ransomware decryption tools:

Encryption algorithms used by most ransomware-type infections are extremely sophisticated and, if the encryption is performed properly, only the developer is capable of restoring data. This is because decryption requires a specific key, which is generated during the encryption. Restoring data without the key is impossible. In most cases, cybercriminals store keys on a remote server, rather than using the infected machine as a host. Dharma (CrySis), Phobos, and other families of high-end ransomware infections are virtually flawless, and thus restoring data encrypted without the developers' involvement is simply impossible. Despite this, there are dozens of ransomware-type infections that are poorly developed and contain a number of flaws (for example, the use of identical encryption/decryption keys for each victim, keys stored locally, etc.). Therefore, always check for available decryption tools for any ransomware that infiltrates your computer.

Finding the correct decryption tool on the internet can be very frustrating. For this reason, we recommend that you use the No More Ransom Project and this is where identifying the ransomware infection is useful. The No More Ransom Project website contains a "Decryption Tools" section with a search bar. Enter the name of the identified ransomware, and all available decryptors (if there are any) will be listed.

Searching for ransomware decryption tools in nomoreransom.org website

Restore files with data recovery tools:

Depending on the situation (quality of ransomware infection, type of encryption algorithm used, etc.), restoring data with certain third-party tools might be possible. Therefore, we advise you to use the Recuva tool developed by CCleaner. This tool supports over a thousand data types (graphics, video, audio, documents, etc.) and it is very intuitive (little knowledge is necessary to recover data). In addition, the recovery feature is completely free.

Step 1: Perform a scan.

Run the Recuva application and follow the wizard. You will be prompted with several windows allowing you to choose what file types to look for, which locations should be scanned, etc. All you need to do is select the options you're looking for and start the scan. We advise you to enable the "Deep Scan" before starting, otherwise, the application's scanning capabilities will be restricted.

Recuva data recovery tool wizard

Wait for Recuva to complete the scan. The scanning duration depends on the volume of files (both in quantity and size) that you are scanning (for example, several hundred gigabytes could take over an hour to scan). Therefore, be patient during the scanning process. We also advise against modifying or deleting existing files, since this might interfere with the scan. If you add additional data (for example, downloading files/content) while scanning, this will prolong the process:

Recuva data recovery tool scan time

Step 2: Recover data.

Once the process is complete, select the folders/files you wish to restore and simply click "Recover". Note that some free space on your storage drive is necessary to restore data:

Recuva data recovery tool recovering data

Create data backups:

Proper file management and creating backups is essential for data security. Therefore, always be very careful and think ahead.

Partition management: We recommend that you store your data in multiple partitions and avoid storing important files within the partition that contains the entire operating system. If you fall into a situation whereby you cannot boot the system and are forced to format the disk on which the operating system is installed (in most cases, this is where malware infections hide), you will lose all data stored within that drive. This is the advantage of having multiple partitions: if you have the entire storage device assigned to a single partition, you will be forced to delete everything, however, creating multiple partitions and allocating the data properly allows you to prevent such problems. You can easily format a single partition without affecting the others - therefore, one will be cleaned and the others will remain untouched, and your data will be saved. Managing partitions is quite simple and you can find all the necessary information on Microsoft's documentation web page.

Data backups: One of the most reliable backup methods is to use an external storage device and keep it unplugged. Copy your data to an external hard drive, flash (thumb) drive, SSD, HDD, or any other storage device, unplug it and store it in a dry place away from the sun and extreme temperatures. This method is, however, quite inefficient, since data backups and updates need to be made regularly. You can also use a cloud service or remote server. Here, an internet connection is required and there is always the chance of a security breach, although it's a really rare occasion.

We recommend using Microsoft OneDrive for backing up your files. OneDrive lets you store your personal files and data in the cloud, sync files across computers and mobile devices, allowing you to access and edit your files from all of your Windows devices. OneDrive lets you save, share and preview files, access download history, move, delete, and rename files, as well as create new folders, and much more.

You can back up your most important folders and files on your PC (your Desktop, Documents, and Pictures folders). Some of OneDrive’s more notable features include file versioning, which keeps older versions of files for up to 30 days. OneDrive features a recycling bin in which all of your deleted files are stored for a limited time. Deleted files are not counted as part of the user’s allocation.

The service is built using HTML5 technologies and allows you to upload files up to 300 MB via drag and drop into the web browser or up to 10 GB via the OneDrive desktop application. With OneDrive, you can download entire folders as a single ZIP file with up to 10,000 files, although it can’t exceed 15 GB per single download.

OneDrive comes with 5 GB of free storage out of the box, with an additional 100 GB, 1 TB, and 6 TB storage options available for a subscription-based fee. You can get one of these storage plans by either purchasing additional storage separately or with Office 365 subscription.

Creating a data backup:

The backup process is the same for all file types and folders. Here’s how you can back up your files using Microsoft OneDrive

Step 1: Choose the files/folders you want to backup.

Click the OneDrive icon in the taskbar

Click the OneDrive cloud icon to open the OneDrive menu. While in this menu, you can customize your file backup settings.

Select Help & Settings and click Settings

Click Help & Settings and then select Settings from the drop-down menu.

Select the Backup tab and click Manage backup

Go to the Backup tab and click Manage backup.

Select folders to backup and click Start backup

In this menu, you can choose to backup the Desktop and all of the files on it, and Documents and Pictures folders, again, with all of the files in them. Click Start backup.

Now, when you add a file or folder in the Desktop and Documents and Pictures folders, they will be automatically backed up on OneDrive.

To add folders and files, not in the locations shown above, you have to add them manually.

Select a file manually and copy it

Open File Explorer and navigate to the location of the folder/file you want to backup. Select the item, right-click it, and click Copy.

Paste the copied file in the OneDrive folder to create a backup

Then, navigate to OneDrive, right-click anywhere in the window and click Paste. Alternatively, you can just drag and drop a file into OneDrive. OneDrive will automatically create a backup of the folder/file.

File statuses in OneDrive folder

All of the files added to the OneDrive folder are backed up in the cloud automatically. The green circle with the checkmark in it indicates that the file is available both locally and on OneDrive and that the file version is the same on both. The blue cloud icon indicates that the file has not been synced and is available only on OneDrive. The sync icon indicates that the file is currently syncing.

Click Help & Settings and click View Online

To access files only located on OneDrive online, go to the Help & Settings drop-down menu and select View online.

Click the Settings cog and click Options

Step 2: Restore corrupted files.

OneDrive makes sure that the files stay in sync, so the version of the file on the computer is the same version on the cloud. However, if ransomware has encrypted your files, you can take advantage of OneDrive’s Version history feature that will allow you to restore the file versions prior to encryption.

Microsoft 365 has a ransomware detection feature that notifies you when your OneDrive files have been attacked and guide you through the process of restoring your files. It must be noted, however, that if you don’t have a paid Microsoft 365 subscription, you only get one detection and file recovery for free.

If your OneDrive files get deleted, corrupted, or infected by malware, you can restore your entire OneDrive to a previous state. Here’s how you can restore your entire OneDrive:


1. If you're signed in with a personal account, click the Settings cog at the top of the page. Then, click Options and select Restore your OneDrive.

If you're signed in with a work or school account,  click the Settings cog at the top of the page. Then, click Restore your OneDrive.

2. On the Restore your OneDrive page, select a date from the drop-down list. Note that if you're restoring your files after automatic ransomware detection, a restore date will be selected for you.

3. After configuring all of the file restoration options, click Restore to undo all the activities you selected.

The best way to avoid damage from ransomware infections is to maintain regular up-to-date backups.

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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 pcrisk.com 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.

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Malware activity

Global malware activity level today:

Medium threat activity

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

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