Anti-virus companies are benefiting from the growth in malicious software. Analyst firm Gartner said that the industry has grown 13.6 percent in 2005, with revenue totalling $4 billion.

Future prospects for the market are looking good, too, as Gartner predicts double-digit growth in the short term. The strongest growth is occurring in Canada, followed by the Middle East and Africa and the Asia/Pacific regions, Gartner said.

Vendors are expected to add security features to software, such as anti-spyware and firewall functions, as the competing products become more closely matched in performance, said Nicole Latimer-Livingston, principal research analyst.

"The market for stand-alone anti-virus and anti-spyware products for businesses and consumers will eventually start to decline as interest for end-point security product suites continues to grow," Latimer-Livingston wrote in a commentary.

Symantec holds a majority of the market at 53.6 percent, followed by McAfee at 18.8 percent and Trend Micro at 13.8 percent. All three vendors were down over their 2004 market share, but just slightly, with none losing more than 1 percent.

Gartner said its market figures are now calculated in terms of total product revenue to account for hosted and subscription offerings as well as open-source software. Previously, Gartner measured market share in terms of new licence revenue.

Panda Software was the fastest growing anti-virus company between 2004 and 2005, expanding by 23.8 percent to take 3.2 percent of the market. It's a distant fourth place, but it is strong in the European small and medium-size business market, Gartner said.

All vendors could be affected by Microsoft, which now has consumer and enterprise security products. Earlier this month, Microsoft launched Live OneCare, its consumer firewall, anti-virus and back-up software. To sweeten the deal, Microsoft is offering three PC licenses for US$49.95 per year.

"Microsoft's entry into the consumer antivirus market is expected to unleash stronger price competition, which will likely lower the overall market revenue opportunity," Latimer-Livingston wrote.

This month Microsoft rebranded its enterprise software as "Forefront," which includes Antigen, enterprise anti-virus and anti-spam software and Forefront Client Security, an early beta release that provides anti-virus protection across business desktops, laptops and server operating systems.

Gartner said the enterprise share of the anti-virus market in 2005 was 51.5 percent while the consumer segment came in at 48.5 percent.