Security researchers have warned users of the Trillian instant messaging client that the software harbours three critical vulnerabilities that could be used to hijack their Windows PCs.

Trillian's developer, Cerulean Studios, has updated the IM client version to to patch the bugs.

The vulnerabilities were reported by 3Com's TippingPoint , which posted advisories for each. Danish bug tracking firm Secunia, meanwhile, collectively ranked the three as "highly critical" problems, its second-highest threat rating.

The bugs include one within the header parsing code for Microsoft's MSN instant messaging protocol, said TippingPoint's alerts. Another involves how Trillian's talk.dll parses XML data, and a third is within messages sent via America Online's AIM instant messaging network.

The first two can be exploited by attackers without tricking the user into helping - simply receiving a maliciously-crafted message triggers those bugs - but the third requires recipients to open a malformed image file, said TippingPoint. All three could be used by hackers to remotely inject their own code onto the PC, added the security company.