It's Windows vs. Windows as Microsoft battles piracy

In an effort to boost sales of Windows, Microsoft has its sights set on its nearest competitor.

But it's not Linux. And sorry, Apple Computer fans, it's not the Mac.

The biggest rival to Windows sales is Windows itself--or rather pirated copies of the OS. And Microsoft is starting to put its foot down. In its most serious bid yet to reap revenue from those who've been getting Windows without payment to Microsoft, the company plans to require computer owners to verify that their copy of Windows is properly licensed before allowing them to download software from Microsoft's site. By mid-year, the once voluntary Windows Genuine Advantage program will become mandatory.

Those with unlicensed copies of Windows will be blocked from getting both add-ons to the OS and security patches through Microsoft's download site (though they will still be able to use the Automatic Update feature built into Windows).