Microsoft (NASDAQ:MSFT) is getting serious about security. Finally.

Mr. Softy yesterday introduced Security Essentials, free software designed to protect Windows users from viruses, spyware, and other malware. "It's easy to tell if your PC is secure -- when you're green, you're good. It's that simple," Microsoft says at its download page for Security Essentials.

If you're thinking that sounds a lot like what Symantec (NASDAQ:SYMC), McAfee (NYSE:MFE), and Trend Micro already offer, you aren't alone. Blogger Dave Hunter mocked those who dismiss Security Essentials as too lightweight to command a premium:

That may well be classified as whistling past the graveyard since very little trumps free andĀ if Windows Security Essentials is as good as the beta reviews indicated, the security vendors may have a real problem. I'm still waiting for one or more of them to drop a dime to the antitrust regulators in the US or EU.

Ouch.

But he's right: Microsoft's competitors tend to run to regulators when a threat surfaces. Look at the browser market. Both Opera Software and Google (NASDAQ:GOOG) have complained to the European Union about Internet Explorer.

Symantec and McAfee probably have less to worry about, if only because both long ago diversified beyond PC security. McAfee bought Secure Computing last year, adding heft to its portfolio of tools for locking down networks. Symantec competes with EMC (NYSE:EMC) and Hewlett-Packard (NYSE:HPQ) in storage and data backup, thanks to its acquisition of Veritas five years ago.

Still, we shouldn't discount the importance of PC security. Gartner estimates that security software vendors collected roughly $12 billion in 2008 revenue. Symantec had the largest share with 22% of the market. Microsoft managed 2.3%, thanks to its OneCare package that few considered a reasonable substitute for what Symantec and McAfee offer.

That's no longer true, early reviews are positive, and Microsoft is offering a free solution this time. Now, Mr. Softy is playing at the major league level -- and you can bet that he's playing to win.

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