The software, initially code-named Morro, is said to protect PCs against malware, computer viruses, and spyware. Microsoft replaced its subscription-based Windows Live OneCare with Morro after discontinuing OneCare in June.

Microsoft Security Essentials is ideal for low-bandwidth scenarios or less-powerful PCs, according to the company. By targeting the core anti-malware features that most consumers do not keep up to date, the software behemoth said, it will provide the essential protection that consumers need without overusing system resources.

Not a Suite

The Redmond, Wash.-based company said making the software available free is about taking down cost barriers that in the past have stopped customers from purchasing up-to-date security protection for their PCs.

"Security has always been one of the big issues surrounding Windows, so it makes sense for Microsoft to make it easy as well as cheap for Windows users to be protected," said Michael Gartenberg, an Interpret analyst.

Microsoft is also quick to remind potential users that the Security Essentials software is not a security suite that provides rich PC -tuning capabilities or backs up data.

"But if what you are looking for is 'install and forget' malware protection and solid quality, Microsoft Security Essentials may be just what you have been waiting for," the Microsoft Security Essentials team wrote in an official blog. Because it's free, no registration is required and no personal information is collected, according to Microsoft.

The software, which is available in eight languages and in 19 markets for Windows PCs, runs in the background so PC users are able to work without interruptions or long waits.

Wiping Out Competition

While Microsoft said its security software is to protect PC users, the free software may also wipe out the need to pay for other security software, including those from Arbor Networks, Symantec and McAfee.

When Microsoft first introduced the beta version of Security Essentials, analysts said the move would cause sleepless nights for competitors McAfee and Symantec, who would be worried about users switching from paid-for to free software.

"Microsoft has not been troubled in the past about adding features to Windows at the expense of third parties to make Windows users' lives better, so this move totally makes sense," Gartenberg said.

But Microsoft said Security Essentials was not developed to wipe out the use of other security software. "Free anti-malware is not new," said spokesperson Mac Brown. "Many other vendors provide antivirus solutions at no cost. By adding our free, slimmed-down core anti-malware solution, we believe that we can help address those consumers who want and know they need core anti-malware protection but either cannot afford a full security suite or don't have access to payment instruments like credit cards required for online subscriptions."

The free software release comes just weeks before Microsoft's new Windows 7 operating system will hit store shelves. It's unclear if Security Essentials will be tied into Windows 7 as its default antivirus software or continue as a stand-alone download.

One thing that is clear is that Microsoft will be walking a tight line if it includes the software protection in Windows 7 after facing $1 billion in fines from the European Commission for including Windows Media Player in a previous version of Windows.