As of January 15, 2003, due to a decreased rate of submissions, Symantec Security Response has downgraded this threat from a Category 4 to a Category 2.
Symantec has not seen any significant increase in activity due to the re-activation of the emailing routine after its initial 10-day sleep period.
W32.Nimda.A@mm is a mass-mailing worm that uses multiple methods to spread itself. The name of the virus came from the reversed spelling of "admin."
- Sends itself by email
- Searches for open network shares
- Attempts to copy itself to unpatched or already vulnerable Microsoft IIS web servers
- Is a virus infecting both local files and files on remote network shares.
The worm uses the Unicode Web Traversal exploit. A patch for computers running Windows NT 4.0 Service Packs 5 and 6a or Windows 2000 Gold or Service Pack 1, as well as information regarding this exploit can be found at http://www.microsoft.com/technet/security/bulletin/ms00-078.asp
When the worm arrives by email, it uses a MIME exploit allowing the threat to be executed by reading or previewing the file. Information and a patch for this exploit can be found at http://www.microsoft.com/technet/security/bulletin/MS01-020.asp
If you visit a compromised Web server, you will be prompted to download a .eml (Outlook Express) email file, which contains the worm as an attachment. You can disable "File Download" in your Internet Explorer Internet Security Zones to prevent this compromise.
Also, the worm will create open network shares on the infected computer, allowing access to the system. During this process, the worm creates the guest account with Administrator privileges.
may be downloaded using LiveUpdate or from the Symantec Security Response
Symantec offers a host of solutions to defend and protect against W32.Nimda.A@mm. Click here
to review Symantec's recommendations on how to address W32.Nimda.A@mm and similar "blended threats."
Information for Macintosh users
Although this worm does not infect Macintosh computers, the worm can be passed through Macintosh email to Windows computers. Also, if you share a network with Windows computers, files could be placed on your hard drive. For additional information, read the document, "Are Macintoshes affected by the Nimda virus?
Information for Novell users
Novell servers are not directly vulnerable, but a Novell client running under Windows can access the Novell server and execute the file from there (using a login script or other means), which can further spread the virus.
Microsoft has released a cumulative roll up for IIS 4.0 on NT 4.0 SP5 and later, as well as all security patches released to date for IIS 5.0. This information can be found at http://www.microsoft.com/technet/security/bulletin/MS01-044.asp
Microsoft has provided information regarding this threat at: http://www.microsoft.com/technet/treeview/default.asp?url=/technet/security/topics/nimda.asp
For information on .enc detections, read the article, What is an .enc detection?
For additional information, read the Microsoft TechNet article, Information on the "Nimda" Worm
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