A worm is being distributed via a picture of a female model which appears on the instant messaging system. Clicking on the link infects the user's computer, by downloading a Trojan which then installs the worm.

A spokesman for computer security firm Sophos said:

"Once it's up and running, the Pykse worm attempts to connect to a number of remote websites, presumably in an attempt to generate advertising revenue for them by increasing their number of 'hits'."