W32.Karimex

SUMMARY

W32.Karimex is a virus that prepends itself to randomly chosen .exe files in the current folder.

Protection

• Virus Definitions (LiveUpdate™ Weekly) October 30, 2002
• Virus Definitions (Intelligent Updater) October 30, 2002

TECHNICAL DETAILS

When W32.Karimex runs, it does the following:

It displays a message that has two buttons,

• If you click the left button, you will see a graphic with Korean characters.
• If you click the right button and the current system date is the 22nd, you will see a message that contains the string "khdo0905@dreamwiz.com." The virus then creates these files:
  • C:RunME.vbs, which is 408 bytes in length
  • C:RunVbs.bat, which is 37 bytes in length

NOTE: These two files are not viral; therefore, Symantec antivirus products do no detect them. Delete them manually if you find them.

The virus creates a nonviral file in the folder in which the virus exists; the file has the same file name as the virus, but with the .vir extension. This file is 90,112 bytes in length.

The virus randomly chooses some .exe files and prepends its viral body, which is 32,767 bytes in length, to the host files. The virus also appends "TTF" to the end of the host file. The virus can reinfect the same file multiple times.

When an infected file runs, you may see the following error message:

"The <host file name> file appears to be corrupt. Reinstall the file, and then try again."

NOTE: The infected file did not infect other files during tests in the Symantec Security Response lab.

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

NOTE: These instructions are for all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Update the virus definitions.
2. Run a full system scan, and delete all files that are detected as W32.Karimex. Replace the infected files with clean backups if necessary. Delete the following files if they exist:
   • C:RunME.vbs,
   • C:RunVbs.bat

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

To update the virus definitions:
All virus definitions receive full quality assurance testing by Symantec Security Response before being posted to our servers. There are two ways to obtain the most recent virus definitions:

• Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions are posted to the LiveUpdate servers once 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 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.

To scan for and delete the infected files:

1. Start your Symantec antivirus program, and make sure that it is configured to scan all files.
   • Norton AntiVirus consumer products: Read the document How to configure Norton AntiVirus to scan all files.
   • Symantec enterprise antivirus products: Read the document How to verify a Symantec Corporate antivirus product is set to scan All Files.
2. Run a full system scan.
3. If any files are detected as infected with W32.Karimex, click Delete. Replace the infected files with clean backups, if necessary.
4. Use Windows Explorer to delete the following files if they exist:
   • C:RunME.vbs
   • C:RunVbs.bat