Threat Explorer

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VBS.A24

VBS.A24

Discovered:
24 August 2000
Updated:
13 February 2007
Also Known As:
VBS/Netlog.g.worm

VBS.A24 is a worm that does little but replicate. It attempts to copy itself across the 24.*.*.* subnet. Any shared drives found on this subnet are subject to infection.

The worm also attempts to remove a VBS.Network infection from the system.

Antivirus Protection Dates

  • Initial Rapid Release version 05 September 2000
  • Latest Rapid Release version 28 September 2010 revision 054
  • Initial Daily Certified version 05 September 2000
  • 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.

VBS.A24 first checks for the existence of the Network.VBS file. If this file is located at C:\ or C:\Windows\Start Menu\Programs\Startup, it is deleted. Norton AntiVirus detects the Network.VBS file as VBS.Network.

To copy itself, the worm selects a random IP address found on the 24.*.*.* subnet (e.g., 24.150.1.19) and searches for shared drives. If it finds a shared drive, the drive is mapped locally on the currently infected computer.

The worm then copies itself to the shared drive (c:\windows\startm~1\programs\startup\) as the file A24.VBS.

Local mappings created by the worm are removed after the worm has executed.

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 the worm from the computer, delete all files Norton AntiVirus detects as VBS.A24. These files are located in the \Windows\Start Menu\Programs\Startup directory.

It is also recommended that you disable sharing on the computer if it is not necessary.

Writeup By: Brian Ewell