Although some Linux antivirus software is now available, vendors are waiting for a major attack before pushing their wares.

Many have developed Unix antivirus products, but are only now moving to Linux to deal with potential threats to businesses running both Windows and open source software.

Network Associates recently released its first Linux server antivirus software, citing the need to stop the transmission through Linux servers of malicious code aimed at Windows.

"Linux has been inherently more secure than Microsoft and the latter has also been targeted more heavily," said Roger Levenhagan, managing director of Trend Micro UK.

"But the full force of the antivirus industry won't be devoted until Linux gets hit hard by a virus, and then consumers will demand it.

"We have products out there that address open source software but all the emphasis is still against Microsoft in the short term."

The ADM worm was the first virus aimed specifically at Linux users and appeared briefly in 1998. Symantec reported that it has found three Linux viruses in the wild since the start of 2004.

Symantec chief executive John Thompson confirmed in a statement that his company would "deliver a Linux desktop antivirus solution to the market" at some point this year, but did not give a time scale for development.

Graham Cluley, senior technology consultant at Sophos, added: "Linux has a better history for security than Microsoft, and hackers are more focused on Microsoft.

"So the main demand for Unix antivirus software comes from companies running Windows on a Unix server trying to boost security. The same may be true for Linux."