Security Essentials helps protect a PC against viruses, spyware, Trojans, rootkits and other harmful software. The free service is expected to compete directly with the lower-end offerings of McAfee and Symantec, two of the leading providers of security software.

Regular Signature Updates

Security Essentials will be available for PCs running Windows Vista, XP and the upcoming Windows 7 operating system, and will initially be available for users in U.S., Israel and Brazil, in English and Portuguese.

Last week, the software giant said Morro, as the security program was then called, was being tested internally among employees and would be released at an unspecified point this year.

Microsoft offered similar security software through its Live OneCare, which it said last year would be discontinued. The software giant has announced that retail sales for OneCare will be discontinued by the end of June, with support continuing through the end of current subscriptions. As Security Essentials rolls out, all OneCare sales, including online, will be phased out.

The new Security Essentials can regularly update itself with signatures of new malware through its online signature service. To do so, auto updates will need to be enabled in Windows.

'A Good Thing'

Chris Christiansen, an analyst with industry research firm IDC, described the software as "a good thing" because there are "fairly low levels" of security subscription rates among PC users.

According to industry observers, this has been a concern at Microsoft because PCs have been getting infected, and it has been impacting the Microsoft experience as well as the operating system's reputation. Some analysts have also noted that signature-based antivirus software has basically become a commodity, where the distinguishing feature is price.

Christiansen noted that Security Essentials provides "a basic level of security," adding that, to get "fairly reasonable" security, one should also use a firewall and, if children can use the computer, software for content filtering.

The free software, he said, will have a "fairly good level of quality," although users should make sure to remove other versions of antivirus software.

"Multiple antiviral software often don't work well together," he said, adding that having two such programs on your PC could "be worse than having none." Security Essentials will not automatically remove other programs.

He also pointed out that Security Essentials doesn't completely replicate OneCare, because, among other things, it doesn't replicate the archiving functionality for backing up documents. It also doesn't provide a firewall, or the ability to manage more than one PC.