Threat Explorer

The Threat Explorer is a comprehensive resource consumers can turn to for daily, accurate, up-to-date information on the latest threats, risks and vulnerabilities.



10 February 1995
13 February 2007
Also Known As:
CMOS4, D3, NewBug, New Bug
Systems Affected:

AntiEXE is a virus that infects the master boot record (MBR) and DOS boot sectors (DBS). AntiEXE spreads only when there is an attempt to boot the system from an infected floppy disk.

During the boot process, AntiEXE loads the MBR into memory and checks for infection. If it determines that the MBR is not infected, then AntiEXE stores the uninfected MBR at cylinder 0, side 0, sector 13 on the hard disk. AntiEXE then places its virus code into the MBR and writes the infected MBR back to the hard disk at cylinder 0, side 0, sector 1.

After the boot process is complete and AntiEXE is active in memory, then AntiEXE displays its stealthing capabilities by redirecting any disk reads of the infected MBR or DBS to their clean counterparts. (On floppy disks, the original DBS is stored in the last sector of the root directory.) Along with stealthing the reads of the MBR or DBS during all disk-read operations, AntiEXE searches for a specific .exe file, whose identity remains unknown, and corrupts the file if it is found.


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 AntiEXE virus:
To remove AntiEXE, you must boot the computer using a uninfected external source, such as a bootable floppy disk or bootable CD, and then run a virus scan. For this purpose, you can use Norton AntiVirus Rescue disks or Norton AntiVirus Emergency Disks.

NOTE : The Norton AntiVirus Emergency Disk set is available as a free download. For instructions on how to obtain and use it, see the document How to create Norton AntiVirus Emergency Disks .