Mac OS X remains untouched by the recent wave of viruses to have hit Windows systems, reports say.

In the past ten days three viruses have struck Windows systems: the Blaster worm, the Sobig F virus and the Welchi virus, which tried to proof systems against Blaster but was flawed.

The Blaster worm even affected the US Navy's multi-million-dollar Navy and /Marine Corps Intranet, with some reports claiming this was shut down by the assault, which the military denied.

Market-leading virus OS

Mac Experience author David Zeiler says only 50 classic Mac OS viruses exist, against 70,000 plus viruses that affect Windows: "Virus writers have concentrated on the market leader. They aim viruses at Windows systems because Microsoft has taken 90 per cent plus of the market,' reports SunSpot.Net.

Today, "more than two years after its introduction, not a single Mac OS X-specific virus has yet appeared," writes Zeiler.

With Apple's releasing a System Security update each month and the paucity of viruses for Unix systems, Zeiler writes: "Even neglectful Mac users who ignore all computing safety advice probably will never experience a security problem."

Time-consuming & expensive

Microsoft however issues dozens of software patches, some of which cause their own problems. A Microsoft update released last year for Windows NT crashed entire servers. The company even released a new update for its Internet Explorer browser today to protect against a flaw that could let hackers take over other people's PCs remotely.

Many home users have difficulty keeping up with Microsoft's updates, and IT support groups in the enterprise must spend many hours simply maintaining their existing systems – at great cost to their company's.

The Sobig Windows virus that's currently circulating has emerged as one of the fastest growing viruses ever, the BBC reports. One email filtering firm intercepted over one million copies of it in 24 hours, while AOL has stopped over 11.5 million copies of it since August 18.

This virus sends copies of itself to people in Outlook's address book and tries to implant a background program that turns infected machines into relays for any messages sent by the virus creator.

Many large enterprises and local government departments without email all week in the UK, while overstretched IT support teams struggle to repair the damage, at great global cost to businesses, local and national government departments.

IT tech's profit from virus attacks Noted Mac columnist Robert Cringley last week asked why Macs are not more widely adopted within the enterprise.

"Whatever the conventional wisdom or the Microsoft marketing message, Macs aren't dramatically more expensive to buy and on a Total Cost of Ownership basis they are probably cheaper," he wrote, asking: "Nobody would argue that Macs are harder to use. Clearly, they are easier to use, especially on a network. So what's the problem? Why do Macs seem to exist only in media outfits?"

Cringely concluded that: "Macs threaten the livelihood of IT staffs.

"Ideally, the IT department ought to recommend the best computer for the job, but more often than not, they recommend the best computer for the IT department's job," he said.

Apple recommends all Mac users install anti-virus software as a precautionary measure – and to ensure they do not pass viruses to their poorer, Windows-using contacts.