Instant messaging client Trillian harbours three critical vulnerabilities that could be used to hijack their Windows Pcs, according to 3Com's TippingPoint security unit and bug tracking firm Secunia. TippingPoint has posted advisories for each, while Secunia 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 AOL'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.

Trillian is one of several IM clients that support multiple IM services, and lets users chat with contacts on AOL's, Microsoft 's and Yahoo 's networks, as well as people using ICQ or IRC.

Trillian's developer, Cerulean Studios, has updated the IM client to version to patch the bugs. Version can be downloaded from the Cerulean Studios website. Trillian runs on Windows 98, 2000, ME, XP and Vista.