Information Week wrote:New worms spreading through MSN Messenger -- and its bundled-with-Windows Windows Messenger version -- via links to a malicious site are infecting users and leaving their PCs open to hacker hijack, security vendors reported Monday.
The new worms, tagged as Kelvir.a and Kelvir.b, appeared over the weekend and on Monday, respectively, anti-virus vendors said. Both use the same mechanism to attract users and infect Windows-based PCs: they include a link in the instant message. That link, in turn, downloads a malicious file -- the actual worm, a variant of the long-running Spybot -- which opens a backdoor to the compromised machine.
Kelvir spreads by sending itself to all the MSN/Windows Messenger contacts on the infected PC, and poses as cryptic messages such as "lol! see it! u'll like it!" and "omg this is funny!" The link opens a .pif-formatted file.
.pif files are also often a format-of-choice for mass-mailed worms.
Also on Monday, another worm -- dubbed Sumon.a by U.K.-based Sophos -- was discovered spreading via MSN/Windows Messenger. Sumon, which propagates over peer-to-peer file-sharing networks as well, is much more aggressive. It disables a long list of security software, tries to overwrite the HOSTS file so commonly-accessed security Web sites can't be reached, and picks from a large number of links, including "Fat Elvis! lol!" and "Crazy frog gets killed by train!" to entice downloads.
New IM worms
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Long live Trillian. 
NewScientist wrote:WHERE Microsoft goes, computer viruses are bound to follow. Last week the company announced a new product to makes instant messaging (IM) easier from within Microsoft Office applications such as its Outlook emailer. The same day, an internet security firm warned that IM networks are fast becoming the easiest way to catch a computer virus.
"We're now seeing an outright focus by virus writers on IM," says John Sakoda of IMlogic in Waltham, Massachusetts, which has recorded 26 IM-based viruses on the net this year alone. Fuelling this growth is the burgeoning use of IM itself. Market analyst Gartner expects IM traffic to exceed that of email by 2006.
In an effort to stay one step ahead of the virus writers, Microsoft has built an extra IM server into its Office networks to spot virus-laden messages. But this feature is available only for business users. For home users, the company is plugging security holes and updating its free MSN Messenger software, says Torben Andersen of Microsoft.