MySpace.com pages are being infected with a link to a computer virus, and another may be targeting Skype's text chat for the first time, a Finnish computer security firm said Tuesday.

User pages at the popular social networking site MySpace are being modified by versions of the Zlob Trojan, which is installing code that overlays its own window on top of the page, F-Secure Corp.'s chief researcher Mikko Hypponen wrote in the company's security blog.

Zlob tries to download and run malicious software, or malware, from the internet, and looks to change Internet Explorer web browser settings, default search and home pages.

JARGON

A Trojan is a program that appears to perform one function in order to hide a malicious one. Like the mythological Trojan horse such programs are named after, the deception tricks people into granting them access. A worm is a self-replicating computer program that can spread itself without aid from from another program or a person.

When a MySpace user clicks on the overlaid window, it tries to modify that page with code that includes the Zlob download link.

Warezov links in Skype Chat

In a separate post, Hypponen wrote that F-Secure had received initial reports that attempts are being made to spread another known virus through Skype's text-based instant messaging feature.

Skype is popular, free, voice over Internet Protocol (VoIP) software that also has a text chat feature similar to competing products by Yahoo Inc. and Microsoft Corp.

Skype users had alerted F-Secure that they had received links to files infected with a worm called Warezov.

"Some older Warezov variants have used other instant messaging [clients] in a similar fashion, but not Skype," he wrote.

Warezov harvests e-mail addresses it finds on infected computers and sends itself as an attachment to those recipients. It also tries to download newer versions of itself from the internet.