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The CERT Coordination Center publishes incident notes to provide information about incidents to the Internet community.

W32/Novarg.A Virus

Release Date: January 27, 2004
Last Updated: January 30, 2004


The CERT/CC has been receiving reports of a new mass-mailing virus known as W32/Novarg.A, W32/Shimg, or W32/Mydoom that has been reported to open a backdoor to the compromised system and possibly launch a denial-of-service attack at a fixed time in the future.


The W32/Novarg.A virus attempts to do the following:

  • Modify various Windows registry values so that the virus is run again upon reboot
  • Open a listening TCP port in the range of 3127-3198, suggesting remote access capabilities
  • Install a copy of itself in the C:\Program Files\KaZaA\My Shared Folder\ folder, which will be available for download by KaZaA users

The virus arrives as an email message with a 22,528-byte attachment that has a random filename with a file extension of .cmd, .pif, .scr, .exe, or .bat. The attachment may also arrive as a ZIP archive.

Some messages containing the virus have had the following characteristics:

Subject: <random>
From: <spoofed>
To: <email address>

(The body has been reported to contain one of the following three messages.)

"The message cannot be represented in 7-bit ASCII encoding and has been sent as a binary attachment."

"The message contains Unicode characters and has been sent as a binary attachment."

"Mail transaction failed. Partial message is available."

In addition to the backdoor capabilities, the virus is also believed to have the capability to launch a distributed denial-of-service attack against a specific web site beginning on February 1, 2004. As with other malicious code having mass-mailing capabilities, W32/Novarg.A may cause "collateral" denial-of-service conditions in networks where either (a) multiple systems are infected, or (b) large volumes of infected mail are received.

The CERT/CC is continuing to analyze the malicious code and we will update this Incident Note as more information is confirmed.

Anti-virus vendors have developed signatures for W32/Novarg.A:


In addition to following the steps outlined in this section, the CERT/CC encourages home users to review the "Home Network Security" and "Home Computer Security" documents.

Run and maintain an anti-virus product

While an up-to-date antivirus software package cannot protect against all malicious code, for most users it remains the best first-line of defense against malicious code attacks. Users may wish to read IN-2003-01 for more information on anti-virus software and security issues.

Most antivirus software vendors release frequently updated information, tools, or virus databases to help detect and recover from malicious code, including W32/Novarg.A. Therefore, it is important that users keep their antivirus software up to date. The CERT/CC maintains a partial list of antivirus vendors.

Many antivirus packages support automatic updates of virus definitions. The CERT/CC recommends using these automatic updates when available.

Do not run programs of unknown origin

Never download, install, or run a program unless you know it to be authored by a person or company that you trust. Email users should be wary of unexpected attachments, while users of Internet Relay Chat (IRC), Instant Messaging (IM), and file-sharing services should be particularly wary of following links or running software sent to them by other users since these are commonly used methods among intruders attempting to build networks of distributed denial-of-service (DDoS) agents.

Filter network traffic

Reports to CERT/CC indicate that the virus opens a listening TCP port in the range of 3127-3198. Sites should consider blocking both inbound and outbound traffic to these ports, depending on network requirements, at the host and network level.

If access cannot be blocked for all external hosts, the CERT/CC recommends limiting access to only those hosts that require it for normal operation. As a general rule, the CERT/CC recommends filtering all types of network traffic that are not required for normal operation.

Recovering from a system compromise

If you believe a system under your administrative control has been compromised, please follow the steps outlined in

Steps for Recovering from a UNIX or NT System Compromise


The CERT/CC is tracking activity related to this virus as CERT#25304. Relevant artifacts or activity can be sent to with the appropriate CERT# in the subject line.

Authors: Marty Lindner, Damon Morda, and Chad Dougherty

Copyright 2004 Carnegie Mellon University.

Revision History
January 27, 2004: Initial Release
January 30, 2004: Changed worm references

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