1. Symantec/
  2. Security Response/
  3. Trojan.Exprez.B


Risk Level 1: Very Low

June 12, 2012
November 16, 2012 11:53:56 AM
Trojan, Virus
Infection Length:
Systems Affected:
When the Trojan is executed, it decrypts an .exe, .doc, or .docx file that is appended to its own code. It then saves the file to the current folder and launches the default application for that extension, e.g. Microsoft Word.

When Microsoft Word is closed, the threat deletes the Microsoft Word file that it created.

Next, the Trojan creates the following file that is a copy of the executable part of the threat (i.e. without the appended document):
%UserProfile%\Application Data\Microsoft\[EIGHT RANDOM UPPERCASE CHARACTERS].exe

When the computer restarts, the above file is moved to the following location:

The Trojan then infects all .exe, .doc, and .docx files by encrypting them and appending them to a copy of itself. The infected .doc and .docx files are renamed with a new file extension:

Note: After the threat has been removed from the computer, the file extension for all Microsoft Word files will need to be manually reset. The .exe file extensions will not need to be manually reset.

The Trojan then connects to one of the following command-and-control (C&C) servers:
  • [http://]realis-nitra.sk/admin/user/way[REMOVED]
  • [http://]new.disans.ru/script/way[REMOVED]
  • [http://]attow.com.br/includes/domit/way[REMOVED]
  • [http://]www.zugor-bikes.com/way[REMOVED]

It then attempts to download a .jpg file from one of following URLs, extract encrypted data from it, and update the C&C server list:
  • [https://]forum.4game.com/imag[REMOVED]
  • [https://]forum.perfect-privacy.com/imag[REMOVED]


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.
Writeup By: Branko Spasojevic
Summary| Technical Details| Removal

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