A new version of the Netsky e-mail worm is programmed to launch a distributed denial-of-service attack on peer-to-peer (P-to-P) networks, contains a message blaming users for spreading viruses and says that Netsky's authors want to stop hacking and illegal file trading, anti-virus software companies warned.

Netsky.Q first appeared on Monday and is spreading on the Internet. It is the 17th variant of the worm to be released since Netsky first appeared in February, anti-virus companies said.

The Q variant arrives in e-mail file attachments with .pif (Program Information File) or .zip file extensions. Netsky also tries to exploit a long-patched Microsoft security hole that allows file attachments to be launched automatically when the e-mail message is read, according to F-Secure of Helsinki.

Netsky.Q messages are disguised to look like returned e-mail error messages that might be generated by a company's e-mail servers. For example, messages contain subjects like "Delivery Error," "Error," and "Server Error." When opened, the e-mail displays messages such as "Mail Delivery -- This mail couldn't be displayed" and claim to contain a version of the rejected message as a "binary attachment," enticing users to click on the virus file, F-Secure said.

Like earlier versions of Netsky, the new version installs itself on Windows machines when the file attachment is opened. It also combs the infected machine's hard drive and harvests e-mail addresses from a variety of file types.

Netsky.Q is programmed to mail copies of itself to addresses it finds on March 31, 2004, and April 5, 12, 19 and 26, 2004, said Sophos of Abingdon, U.K.

Computers infected with the new worm variant are also programmed to launch a denial-of-service attack on a number of P-to-P and pirated software Web sites including www.kazaa.com, www.edonkey2000.com and www.cracks.am on April 7, and April 12, 2004, F-Secure said.

A message buried in the worm's code may explain the programmed attacks on P-to-P networks. In the message, the Netsky author or authors claim to represent a benevolent group called "SkyNet Antivirus Team" based in "Russia" and draw distinctions between their creation and other worms that open back doors on infected computers that can be used to relay spam message or facilitate future hacking.

The IDG News Service is a Network World affiliate.