Storm wormin the form of e-mails with attachments that, when opened, loaded malicious software onto victims' PCs, commandeering the machines so they could be used for further attacks.
The new Storm worm variant attacks the machines of unsuspecting users when they open an e-mail attachment, click on a malicious e-mail link or visit a malicious site, said Dmitri Alperovitch, principal research scientist at Secure Computing.
But the twist comes when these people later post blogs or bulletin board notices. The software will insert into each of their postings a link to a malicious Web site, said Alperovitch, who rates the threat as "high."
"We haven't seen the Web channel used before," he said. "In the past, we've seen malicious links distributed to people in a user's address book and made to look like it's an instant message coming from them."
The danger in this most recent case, he added, is that the user is actually posting a legitimate blog or bulletin board notice, unaware that a malicious link has been slipped into the text of the posting.