Threat Explorer

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VBS.Over.Trojan

VBS.Over.Trojan

Discovered:
08 May 2001
Updated:
13 February 2007
Also Known As:
VBS.Trojan.Over, trojan VBS/Over

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.

Antivirus Protection Dates

  • Initial Rapid Release version 08 May 2001
  • Latest Rapid Release version 28 September 2010 revision 054
  • Initial Daily Certified version 08 May 2001
  • Latest Daily Certified version 28 September 2010 revision 036
  • Initial Weekly Certified release date pending
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

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 \Windows\Temporary 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":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • 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.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a 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.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. 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.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.

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.


Writeup By: Serghei Sevcenco