Discovered: June 13, 2002
Updated: February 13, 2007 11:39:18 AM
Also Known As: W32/Perrun-A, PE_PERRUN.A, Win32.Perrun, W32/Perrun, Perrun, W32/Perrun.A
Type: Virus
Systems Affected: Windows


W32.Perrun is a virus that appends itself to .jpeg or .txt files. The malicious content of files that it alters will not spread to other computers. Indications of infection are that .jpg or .txt files will have increased in size by approximately 11KB, and the presence of the file Extrk.exe or Textrk.exe.

The original data will not successfully extract from .jpeg files if the file C:\Windows\System\Shimgvw.dll does not exist on an infected computer.
The original data will not successfully extract from .txt files if the file C:\Windows\Notepad.exe does not exist on an infected computer.

Antivirus Protection Dates

  • Initial Rapid Release version June 13, 2002
  • Latest Rapid Release version September 28, 2010 revision 054
  • Initial Daily Certified version October 31, 2007 revision 003
  • Latest Daily Certified version September 28, 2010 revision 036
  • Initial Weekly Certified release date June 19, 2002

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


Technical Description


If a .jpg or .txt file that has been altered by W32.Perrun is opened on another, uninfected computer, it will not execute malicious actions on that computer because the virus requires the presence of the Extrk.exe or Textrk.exe file for it to execute and append its malicious content to other files.

Upon execution of the viral executable which is detected as W32.Perrun.dr, the virus does the following:

It drops the files:

  • Reg.mp3. This is a registry file that the virus uses to modify the registry.
  • Extrk.exe or Textrk.exe. This is the executable that will be configured in the registry to open all JPEG or TXT files.

Depending upon which variant of W32.Perrun, the virus will perform one of the following actions:

For the variant that appends to JPEG files

Extrk.exe is then configured to open all JPEG files by changing the (Default) value of the registry key

HKEY_LOCAL_MACHINE\Software\Classes\jpegfile\shell\open\command

to

extrk.exe %1

For the variant that appends to TXT files

Textrk.exe is then configured to open all TXT files by changing the (Default) value of the registry key

HKEY_LOCAL_MACHINE\Software\Classes\txtfile\shell\open\command

to

textrk.exe %1


Recommendations

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.


Removal


Update the virus definitions and run a full system scan.

  1. Repair files that are detected as W32.Perrun, and delete files that are detected as W32.Perrun.dr
  2. Restore the (Default) value of the registry key

    HKEY_LOCAL_MACHINE\Software\Classes\jpegfile\shell\open\command

    or

    HKEY_LOCAL_MACHINE\Software\Classes\txtfile\shell\open\command

For details on how to do this, read the following instructions.

To scan with Norton AntiVirus and repair or delete the infected files:
  1. Obtain the most recent virus definitions. There are two ways to do this:
    • Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and are posted to the LiveUpdate servers one time each week (usually Wednesdays) unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, look at the Virus Definitions (LiveUpdate) line at the top of this write-up.
    • Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions have undergone full quality assurance testing by Symantec Security Response. They are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and installed manually. To determine whether definitions for this threat are available by the Intelligent Updater, look at the Virus Definitions (Intelligent Updater) line at the top of this write-up.

      Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.
  2. Start Norton AntiVirus (NAV), and make sure that NAV is configured to scan all files.
  3. Run a full system scan.
  4. If NAV detects any files as infected by W32.Perrun, click Repair.
  5. If NAV detects any files as infected by W32.Perrun.dr, click Delete.

To restore the value to the registry:

CAUTION : Symantec strongly recommends that you back up the registry before you make any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify only the keys that are specified. Read the document How to make a backup of the Windows registry for instructions.
  1. Click Start, and click Run. The Run dialog box appears.
  2. Type regedit and then click OK. The Registry Editor opens.
  3. Depending on the variant, navigate to one of the following keys:

    (If you are not sure of the variant, check both keys.)

    HKEY_LOCAL_MACHINE\Software\Classes\jpegfile\shell\open\command

    or

    HKEY_LOCAL_MACHINE\Software\Classes\txtfile\shell\open\command
  4. In the right pane, double-click

    (Default)

    The Edit String dialog box opens.
  5. Delete the contents of the Value Data box, and replace it with the following:
    • For the jpegfile\shell\open\command key:

      "C:\PROGRA~1\INTERN~1\iexplore.exe" -nohome

      NOTE: This is the default setting for a standard installation that uses Internet Explorer as the program with which .jpg files are opened. If you have changed this--for example, you use another program to view or edit files of this type, you should make the appropriate substitution.
    • For the txtfile\shell\open\command key:

      This varies with the operating system. You may need to look at that same key on a working computer with the same operating system and configuration to determine this. Two common values are:
      • Windows 98: C:\Windows\Notepad.exe %
      • Windows 2000: %SystemRoot%\system32\NOTEPAD.EXE %1

  6. Click Registry, and click Exit.


Writeup By: Douglas Knowles