W32.Perrun

SUMMARY

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:WindowsSystemShimgvw.dll does not exist on an infected computer.
The original data will not successfully extract from .txt files if the file C:WindowsNotepad.exe does not exist on an infected computer.

Protection

• Virus Definitions (LiveUpdate™ Weekly) June 19, 2002
• Virus Definitions (Intelligent Updater) June 13, 2002

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Easy

Damage

• Damage Level: Low
• Payload: Appends to either .jpg or .txt files
• Modifies Files: Appends to either .jpg or .txt files

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

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_MACHINESoftwareClassesjpegfileshellopencommand

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_MACHINESoftwareClasses xtfileshellopencommand

to

textrk.exe %1

Recommendations

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

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended 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 (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• 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.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. 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.

REMOVAL

1. Update the virus definitions and run a full system scan.
2. Repair files that are detected as W32.Perrun, and delete files that are detected as W32.Perrun.dr
3. Restore the (Default) value of the registry key
   
   HKEY_LOCAL_MACHINESoftwareClassesjpegfileshellopencommand
   
   or
   
   HKEY_LOCAL_MACHINESoftwareClasses xtfileshellopencommand

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.
   • NAV Consumer products: Read the document How to configure Norton AntiVirus to scan all files.
   • NAV Enterprise products: Read the document How to verify a Symantec Corporate antivirus product is set 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_MACHINESoftwareClassesjpegfileshellopencommand
   
   or
   
   HKEY_LOCAL_MACHINESoftwareClasses xtfileshellopencommand
   
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 jpegfileshellopencommand key:
     
     "C:PROGRA~1INTERN~1iexplore.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 txtfileshellopencommand 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:WindowsNotepad.exe %
     • Windows 2000: %SystemRoot%system32NOTEPAD.EXE %1
       
       
6. Click Registry, and click Exit.