Threat Explorer

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28 July 1993
13 February 2007

This virus infects files that are in the same folder as the virus, and that have the .com extension. This document describes the Atomic virus, and the Atomic.371 and Atomic.480 variants.

Antivirus Protection Dates

  • Initial Rapid Release version 28 July 1993
  • Latest Rapid Release version 14 December 2018 revision 024
  • Initial Daily Certified version 28 July 1993
  • Latest Daily Certified version 15 December 2018 revision 002
  • Initial Weekly Certified release date pending
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

The Atomic virus infects all .com files that are located in the same folder as the virus by appending its viral body to the host. After infecting the files, the virus displays gibberish characters on the screen.

This variant of Atomic infects all .com files that are located in the same folder as the virus, as well as the C:\ file. The virus overwrites the first 371 bytes of the host, which makes it impossible to repair. After infecting the files, the virus displays the message "Program execution terminated."

This virus is same as Atomic.371, except that the viral body is 480 bytes in length instead of 371 bytes. This virus displays the message "Bad command or file name" instead of "Program execution terminated."


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 virus:
  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. If any files are detected as infected by Atomic, click Repair. If NAV cannot repair the file, you must delete it. Deleted files must be restored from a clean backup.

Writeup By: Keith Smith