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Discovered: November 23, 2015
Updated: August 30, 2016 10:28:16 PM
Also Known As: Unix.Ransomcrypt.B [Symantec]
Type: Trojan
Infection Length: Varies
Systems Affected: Linux

Unix.LinuxEncoder.B is a Trojan horse that encrypts files on the compromised computer and demands payment to decrypt them.

Note: Definitions prior to August, 2016 may detect this threat as Unix.Ransomcrypt.B

Antivirus Protection Dates

  • Initial Rapid Release version November 23, 2015 revision 022
  • Latest Rapid Release version August 03, 2019 revision 007
  • Initial Daily Certified version November 23, 2015 revision 038
  • Latest Daily Certified version August 04, 2019 revision 002
  • Initial Weekly Certified release date November 25, 2015

Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

Technical Description

Once executed, the Trojan creates the following files:

  • /readme.crypto

It then forks itself as a daemon process.

The Trojan then searches for and encrypts files in the following folders:
  • /home
  • /root
  • /var/lib/mysql
  • /var/www
  • /etc/nginx
  • /etc/apache2
  • /var/log

The Trojan also encrypts files in folders that contain the following strings:
  • public_html
  • webapp
  • backup
  • .git
  • .svn

It also encrypts files with the following extensions:
  • .7z
  • .aac
  • .apk
  • .asp
  • .aspx
  • .avi
  • .class
  • .css
  • .csv
  • .db
  • .dll
  • .doc
  • .docx
  • .exe
  • .gif
  • .gz
  • .html
  • .jar
  • .java
  • .jpeg
  • .jpg
  • .js
  • .mov
  • .mp3
  • .mp4
  • .pdf
  • .php
  • .phtml
  • .png
  • .properties
  • .psd
  • .pub
  • .rar
  • .ruby
  • .sql
  • .tar
  • .tgz
  • .tpl
  • .txt
  • .war
  • .wav
  • .wma
  • .wmv
  • .xls
  • .xml
  • .zip

The Trojan adds the following file extension to all the files it encrypts:
  • .encrypted

Next, the Trojan copies the following .txt file into each folder that contains encrypted files:

The .txt file contains a ransom message and payment instructions.


Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.


The following instructions pertain to Symantec AntiVirus for Linux.

  1. Update the virus definitions.
  2. Run a full system scan.

1. To update the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:
  • Running LiveUpdate, which is the easiest way to obtain virus definitions. For Symantec AntiVirus for Linux, LiveUpdate definitions are updated daily.
  • Downloading the definitions using Intelligent Updater. The Intelligent Updater virus definitions are posted daily. You should download the definitions from the Symantec Security Response Web site and manually install them.

2. To run a full system scan

To run a full system scan in Linux, open a command line and type the following:

sav manualscan --scan /

If any files are detected, follow the instructions displayed by your antivirus program.

Writeup By: Mark Anthony Balanza