The virus, which was given the double name Virus.Linux.Bi.a/ Virus.Win32.Bi.a, was reported last week by security firm Kaspersky Lab.

Security researchers worry that the malicious code may be part of a disturbing new trend of viruses that can run on Windows, as well as other operating systems that have been largely ignored by hackers.

"The virus is written in assembler and is relatively simple," Kaspersky says in a posting to the company's Viruslist.com Web site.

"However, it is interesting in that it is capable of infecting the different file formats used by Linux and Windows - ELF and PE format files respectively." (?weblogid=183651915)

The Executable and Linking Format (ELF) and Portable Executable (PE) file formats are used to format certain types of binary files in Linux and Windows, including the .exe and .dll files used in Windows.

The virus appears to have no practical application, Kasperky says. "It is a classic proof-of-concept code, written to show that it is possible to create a cross-platform virus," Kaspersky adds.

"However, our experience shows that once proof-of-concept code is released, virus writers are usually quick to take the code, and adapt it for their own use."

Security training organisation, The SANS Institute, agreed with Kaspersky's assessment, saying that the software should come as a warning to Linux and Mac OS X users who may think their computers are 'invulnerable' to virus threats.

"As the developers of viruses continue to research this, we will see [more] cross platform malware come about in the future," says SANS Internet Storm Center contributor, Swa Frantzen, (http://isc.sans.org/diary.php?storyid=1248&rss)

"Protecting the Linux, Unix and Mac OS X, machines with anti-virus measures is a good thing to start on now if you have not done so already," he adds.