VBS.Trojan.Lovcx

SUMMARY

VBS.Trojan.Lovcx is a Visual Basic Script (VBS) Trojan that is similar to the VBS.Loveletter.CV@mm worm.

The VBS.Trojan.Lovcx Trojan:

1. Copies itself to the WindowsSystem folder as Msword.vbs and Thwin.vbs,
2. Deletes up to five files that have certain file extensions,
3. Saves a list of the deleted files as WindowsSystemListWin.txt, and
4. May also attempt to copy itself to the A drive.

Unlike VBS.Loveletter.CV@mm, VBS.Trojan.Lovcx does not use email to spread itself.

Protection

• Virus Definitions (LiveUpdate™ Weekly) February 26, 2003
• Virus Definitions (Intelligent Updater) February 26, 2003

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: Medium
• Deletes Files: Randomly chooses a file extension from a predetermined list and deletes the first 5 files it finds with that extension.
• Modifies Files: Autoexec.bat

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When VBS.Trojan.Lovcx is executed, it performs the following actions:

1. Copies itself to the %System% folder as these files:
   • Msword.vbs
   • Thwin.vbs
     
     NOTE: %System% is a variable. The Trojan locates the System folder. By default, this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).
     
     
2. Determines the number of the current month and compares it with the number that represents the month in which the VBS.Trojan.Lovcx file was created. If the current month number is either 9 less or 3 more than the created month number, VBS.Trojan.Lovcx does the following:
   1. Adds the following text to the end of the Autoexec.bat file:
      
      @echo off
      rem DEL "&sysdir&"*.SYS
      rem DEL "&sysdir&"*.DLL
      rem DEL "&sysdir&"*.OCX
      rem CLS
      rem FORMAT C: /u /v:UNSCH /autotest
      CLS
      
   2. Creates the value:
      
      THWIN  %System%THWIN.vbs
      
      in these registry keys:
      
      HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
      HKEY_LOCAL_MACHINESoftwareMicrosoftWindows
      CurrentVersionRunServices
      
      so that the Trojan runs when you start Windows. If the second registry keys exist on your computer, the Trojan will run as a service.
      
   3. Creates the value:
      
      Timeout  0
      
      in the registry key:
      
      HKEY_CURRENT_USERSoftwareMicrosoftWindows Scripting HostSettings
      
      
3. Randomly chooses one of the following file extensions:
   • .xls
   • .doc
   • .wav
   • .dwg
   • .mp3
   • .bak
   • .wav
   • .bmp
   • .htm
   • .hlp
   • .chm
   • .jpg
   • .gif
   • .scr
   • .ttf
   • .mid
   • .cdr
   • .mdb
   • .dbf
   • .ico
     
     
4. Deletes the first five files that it finds with the chosen extension. The Trojan saves a list of the files that it deleted in the file, %System%ListWin.txt.

The second time the Trojan runs, it waits 10 minutes, and then attempts to copy itself as Msword.vbs to drive A, if a floppy disk is loaded in the drive.

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

These instructions pertain to 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 the files detected as VBS.Trojan.Lovcx.
3. Delete the values that it added to the registry.
4. Remove the text that it added to the Autoexec.bat file if the computer is running Windows 95/98/Me.
5. Restore the files that the Trojan deleted.
   

For specific details on each of these steps, read the following instructions.

1. Updating 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 the virus definitions. These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate), in the "Protection" section, at the top of this writeup.
• Downloading the definitions using the Intelligent Updater. The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater), in the "Protection" section, at the top of this writeup.
  
  The 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. Scanning for and deleting the infected files

1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
   • For Norton AntiVirus consumer products: Read the document, "How to configure Norton AntiVirus to scan all files."
   • For Symantec AntiVirus Enterprise products: Read the document, "How to verify that 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 VBS.Trojan.Lovcx, click Delete.

3. Deleting the values from 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 the specified keys only. Read the document, "How to make a backup of the Windows registry," for instructions.

1. Click Start, and then click Run. (The Run dialog box appears.)
2. Type regedit
   
   Then click OK. (The Registry Editor opens.)
   
3. Navigate to the key:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
4. In the right pane, delete the value:
   
   THWIN  C:WINDOWSSYSTEMTHWIN.vbs
   
5. Navigate to the key:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindows
   CurrentVersionRunServices
   
   NOTE: This key does not exist on all the systems.
   
6. In the right pane, delete the value:
   
   THWIN  C:WINDOWSSYSTEMTHWIN.vbs
   
   
7. Navigate to the key:
   
   HKEY_CURRENT_USERSoftwareMicrosoftWindows Scripting HostSettings
   
8. In the right pane, delete the following value:
   
   Timeout  0
   
9. Exit the Registry Editor.

4. Removing the text from the Autoexec.bat file
If you are running Windows 95/98/Me, follow these steps:

1. The function you perform depends on your operating system:
   • Windows 95/98: Go to step b.
   • Windows Me: If you are running Windows Me, the Windows Me file-protection process may have made a backup copy of the Win.ini file that you are to edit. If this backup copy exists, it will be in the C:WindowsRecent folder. Symantec recommends that you delete this file before you continue with the steps in this section. To do this:
     • Start Windows Explorer.
     • Browse to and select the C:WindowsRecent folder.
     • In the right pane, select the Win.ini file and delete it. The Win.ini file will be regenerated when you save your changes to it in step f.
       
2. Click Start, and then click Run.
3. Type the following:
   
   edit c:autoexec.bat
   
   And then click OK. (The MS-DOS Editor opens.)
   
   NOTE: If Windows is installed in a different location, make the appropriate path substitution.
   
4. Near the end of the file, look for the following text and delete it if found:
   
   @echo off
   rem DEL "&sysdir&"*.SYS
   rem DEL "&sysdir&"*.DLL
   rem DEL "&sysdir&"*.OCX
   rem CLS
   rem FORMAT C: /u /v:UNSCH /autotest
   CLS
   
5. Click File, and then click Save.
6. Click File, and then click Exit.

5. Restoring the files deleted by the Trojan

1. Using Windows Explorer, locate and double-click the %System%ListWin.txt file. This file contains a list of the files that the worm deleted.
2. If any of the files in the list are files that you need, replace them from clean backup copies.
3. Optional step: Delete the ListWin.txt file.