VBS.Avm

SUMMARY

VBS.Avm is a VBScript virus that attempts to copy itself to .vbs files on the infected computer. The virus also uses Microsoft Outlook to send email to an anonymous email address and to an antivirus researcher.

Behavior

Symptoms

Transmission

Protection

• Virus Definitions (Intelligent Updater) September 21, 1999

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

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When executed, the virus uses Microsoft Outlook to send email to the authors of the virus. The email contains the IP address of the infected computer. The virus also emails a humorous message to a known antivirus researcher.

The virus attempts to append itself to all .vbs files in the current path, WindowsDesktop, StartUp, MyDocuments, and all root folders. The virus creates a copy of itself in the Windows folder as Avm.vbs and it adds the value

AVM

to the registry key

HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun

The virus is executed each time that the computer is started. This virus was originally dropped by the W97M.Coldape macro virus, but it can spread independently.

Variant Information
Variants have been found to consist of only the email routine, only the replication routine, and both the email and replication routine.

Microsoft Word documents infected with the W97M.Coldape virus may be detected as VBS.Avm. These documents are corrupted and must be replaced with known clean backups.

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

To remove this virus from the computer, you need to scan for and delete infected files, and then remove the registry entry that was created by the virus.

To delete infected files:
Files infected by VBS.Avm cannot be repaired and must be deleted.

1. Run LiveUpdate to make sure that you have the most recent virus definitions.
2. Start Norton AntiVirus (NAV), and then run a full system scan, making sure that NAV is set to scan all files.
3. If any files are detected as infected by VBS.Avm, click Delete.

To edit the registry:

CAUTION: We strongly recommend that you back up the system registry before making any changes. Incorrect changes to the registry could result in permanent data loss or corrupted files. Please make sure you modify only the keys specified. Please see the document How to back up the Windows registry before proceeding.

1. Click Start, and click Run. The Run dialog box appears.
2. Type regedit and then click OK. The Registry Editor opens.
3. Navigate to the following subkey:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   
4. In the right pane, select the following value, press Delete, and then click Yes to confirm:
   
   AVM
   
5. Click Registry and then click Exit to save the changes and close the Registry Editor.
6. Restart the computer.