Kaspersky Labs is reporting a new proof-of-concept virus capable of infecting both Windows and Linux systems.

The cross-platform virus is relatively simple and appears to have a low impact, according to Kaspersky. Even so, it could be a sign that virus writers are beginning to research ways of writing new code capable of infecting multiple platforms, said Shane Coursen, senior technical consultant at Kaspersky.

In a note on its Web site, the SANS Internet Storm Center (ISC) in Bethesda, Md,. said the new virus “is a sign the cross-platform aspects are becoming important. As the developers of viruses continue to research this, we will see more cross-platform malware come about in the future.”

The new virus, which Kaspersky calls Virus.Linux.Bi.a/Virus.Win32.Bi.a, is written in assembler and infects only those files in the current directory. “However, it is interesting in that it is capable of infecting the different file formats used by Linux and Windows,” Kaspersky said.

“It isn’t surprising that we are seeing a multiplatform virus,” given the growing popularity of Linux on enterprise desktops, Coursen said. “This is simply proof-of-concept code to show this kind of thing can be done.”

The new virus shows that malicious hackers may be exploring ways of getting new systems into bot networks, according to Johannes Ullrich, chief technology officer at the SANS ISC. But crafting such multi-platform malware is not particularly easy, he said.

“Writing a cross-platform worm is difficult because it limits you to functions that are available on both operating systems,” Ullrich said. “You have to also code the virus in assembly to make it work without relying on any OS-specific function,” he said.

The relatively small number of systems running on non-Windows platforms also makes it less appealing for hackers to go to the trouble of crafting cross-platform viruses, he said.

Though rare, this is not the first instance of such a virus appearing in the wild. In 2001, the sadmind/ISS worm exploited a hole in Sun Microsystems Inc.’s Solaris to infect systems running vulnerable versions of the operating system. Infected systems then scanned for and attacked servers running Microsoft Corp.’s IIS Web server software. That same year, another proof-of-concept virus named Winux infected both Windows and Linux systems.

“Even today, Web sites sending exploits to their visitors tend to detect what browser/platform the visitor is using and send a matching exploit to install some malware,” SANS said in its note.

It’s important for enterprises to be aware of such issues and implement anti-virus tools for protecting non-Windows operating systems if they haven’t done so already, Ullrich said.

“For those thinking their “pet” computer is invulnerable to the virus threat -- it’s not,” SANS said.