Anti-virus companies warn of Shockwave worm

CUPERTINO, California (CNN) -- Computer users who think they are downloading an Internet movie may instead be spreading a new computer worm that spreads through Microsoft Outlook e-mail.

Several anti-virus companies are giving a medium- to high-risk rating to the worm, which has aliases including "Prolin" and "Creative."

"This worm has a lot of characteristics of other recent outbreaks, because it spreads to every name in a user's Outlook address book," said Vincent Weafer, director of Symantec's Anti Virus Research Center. Symantec has assigned a medium risk to Prolin.

The worm shows up as an e-mail with the subject line "A great Shockwave flash movie." The body of the e-mail tells the reader to "check out this new flash movie that i downloaded just now.. It's Great Bye."

Shockwave is a popular Internet animation format with the capability to produce glitzy graphics.

Unlike a virus, a worm can propagate itself over a network, reproducing itself as it goes. A virus cannot infect other computers without assistance.

The e-mail includes the attachment creative.exe. When opened, the worm finds and alters all .JPG and .ZIP files on the user's system and forwards a copy of itself to everyone in the user's e-mail address book.

Weafer said Prolin first appeared Thursday. Many corporations quickly set up filters, he said, but because the worm spreads rapidly through each user's address book the worm is difficult to wipe out completely.

While thousands of viruses circulate at any given time, anti-virus companies like Symantec, McAfee, and TrendMicro say the holidays are prime time for viruses, worms, and hoaxes. Basic warnings to all computer users include:

• Never open an attachment from an unknown person
• Update anti-virus software weekly
• If using a DSL or cable modem, install a personal firewall.

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