Hackers have released a sample code for a virus that could infect both Linux and Windows PCs.The virus, which was given the double name Virus.Linux.Bi.a\/Virus.Win32.Bi.a, was reported Friday by security firm Kaspersky Lab. Security researchers worry 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 wrote in a posting to the company\u2019s Viruslist.com website. "However, it is interesting in that it is capable of infecting the different file formats used by Linux and Windows\u2014ELF and PE format files, respectively."The ELF (executable and linking format) and PE (portable executable) 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, Kaspersky said. "It\u2019s a classic proof-of-concept code, written to show that it is possible to create a cross-platform virus," Kaspersky said. "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 organization The SANS Institute agreed with Kaspersky\u2019s assessment, saying 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," wrote SANS Internet Storm Center contributor Swa Frantzen, in a Friday Web posting."Protecting the Linux, Unix and Mac OS X machines with antivirus measures is a good thing to start on now if you haven\u2019t done so already," he added.-Robert McMillan, IDG News ServiceCheck out our CIO News Alerts and Tech Informer pages for more updated news coverage.