Problem solve Get help with specific problems with your technologies, process and projects.

Top virus threats, part two: Nimda

The effects and fixes for the Nimda virus.

Viruses are not all created equal. Some cause more damage and some spread quickly to a large number of systems. Fortunately, there are only a few viruses that cause lots of damage and spread quickly. Therefore, most viruses are not a big threat. However, those few viruses that are a serious threat is all the reason you need for a multi-level virus protection and removal system.

To help you understand why virus protection is necessary, let's take a quick look at one of the top four viruses currently found in the wild ("in the wild" means actively infecting computers around the world via the Internet or other means).

The virus that is generally considered to be the second-worst virus currently circulating networks across the globe is the W32.Nimda.A@mm virus. Nimda's threat comes from its ability to distribute itself through several means and share the hard drives of infected systems with the Internet. Nimda can attach itself to Microsoft based outgoing e-mail, infect IIS servers and systems via a Web site download, and it can be spread system to system via infected file movements. Once a system is infected, the virus can be easily spread to other systems via file transfers, e-mail messages or the presence of IIS on the system. Plus, with shared local drives, just about anyone can access and download any file off of your PC. Obviously, this is a threat both to productivity and confidentiality.

The Nimda virus gets its name from spelling admin backwards. This is appropriate since the virus enables the guest account and grants it administrative privileges.

If you visit an infected Web server, you'll be prompted to download a file with the extension .eml. This is an Outlook Express file. You should not download this file.

IIS servers can be hardened against Nimda by applying the patch available from Microsoft at

Windows systems can be protected from e-mail, Web and file transfer infection paths by applying the patch available from Microsoft at

The reason this virus is able to spread so quickly is due to the number of Windows PCs and IIS systems that are not properly protected against the simple exploits this virus uses. The virus itself does little damage to an infected system, but it opens doors so that intruders can compromise your systems and even steal your data.

Most antivirus products are able to detect, remove and disable this virus. However, if your system is already infected, you need to manually clean up its artifacts to guarantee that you will not remain infected or accidentally infect others. For details on reversing the changes to systems infected by the W32.Nimda.A@mm virus, please see the Symantec's documentation regarding this virus at

Or the Computer Associates' documentation at

For more information on this virus, other recent viruses and virus top ten lists, see, in addition to the above sites:
The McAfee site:
And the Trend Micro site:

About the author
James Michael Stewart is a researcher and writer for Lanwrights, Inc.

This was last published in April 2002

Dig Deeper on Malware, virus, Trojan and spyware protection and removal

Start the conversation

Send me notifications when other members comment.

Please create a username to comment.