VBS.Over.Trojan

SUMMARY

VBS.Over.Trojan is a Visual Basic Script Trojan horse. If the infected HTML page is opened and the script is allowed to run, the Trojan attempts to overwrite several system files.

Protection

• Virus Definitions (Intelligent Updater) May 8, 2001

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

If the security settings in Internet Explorer are set correctly, then every time that the infected HTML page is opened, the browser will warn you that some software on the page might be unsafe, with the recommendation to not run it. If you allow the software to run, the VBS.Over.Trojan attempts to overwrite the following files:

• Win.com
• Win.ini
• System.ini
• User.exe
• Rundll.exe
• Rundll32.exe
• Emm386.exe
• Ios.ini
• Explorer.exe

NOTE: When attempting to overwrite these files, VBS.Over.Trojan looks for them only in the folder that is parent to the folder from which VBS.Over.Trojan is running. In most cases, by default, the Trojan runs from the WindowsTemporary Internet Files folder; this means that Windows is the parent folder, and most of the target files are located in that folder.

In addition, it attempts to rewrite the C:Command.com file.

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 Trojan:

1. Run LiveUpdate to make sure that you have the most recent virus definitions.
2. Start Norton AntiVirus (NAV), and run a full system scan, making sure that NAV is set to scan all files.
3. Delete any files detected as VBS.Over.Trojan.
4. Any files corrupted by the Trojan should be restored from a clean backup or reinstalled.