Bizex could signal the first of many viruses that spread via instant messaging (IM) software, experts have warned.

Companies should ensure that only those with a legitimate business purpose are allowed access to instant messaging to reduce the risk, according to Graham Cluley, senior technology consultant at antivirus company Sophos.

"Most computer users are now aware of the risk of email viruses and many businesses use internet and gateway-level email scanners to protect their networks from malicious code. But Bizex is a reminder that viruses do not just spread by email," he said.

Bizex spreads via ICQ and encourages users to go to a website to view a cartoon. But when they do their PC is attacked and the worm attempts to steal financial information.

Phil Huggins, chief technologist at security firm IRM, warned: "We're expecting a lot more viruses to be propagated in this way. Open instant messaging systems are being deployed in an increasing number of businesses. Virus creators aim to use every popular technology."

To date the most notable virus spread via an IM program was Goner in 2001. It spread as a screensaver and infected numerous organisations, including Nasa.