Microsoft will launch a public beta of its anti-malware service, Microsoft Security Essentials, on Tuesday as it phases out its Live OneCare suite in favor of a simpler free consumer security offering.

Microsoft Security Essentials, which will run on Windows XP, Vista, and Windows 7, will be available in the U.S., Brazil, and Israel in English and Brazilian Portuguese. A public beta version for Simplified Chinese will be available later in the year.

The service works like traditional antivirus products in which client software monitors programs on a PC. When something changes on the computer, such as files being downloaded or copied or software trying to modify files, the system checks against a set of malware signatures in the client program to see if the code matches the signature for known malware. If so, it blocks it from getting downloaded.

If no signature match is found, the system will ping the server-based Dynamic Signature Service to see if any new signatures are available and, if so, it removes the malware. If it appears to be new malware, the Dynamic Signature Service may request a sample of the code in order to create a new signature.

The service updates its anti-malware database constantly and publishes new antivirus signatures to Microsoft Update three times a day, Alan Packer, general manager of Microsoft's Anti-Malware team, said in an interview on Thursday.

"The hope is that people who install Security Essentials and enable auto updates in their Windows configuration will be protected" automatically, he said.

The service also includes new technologies that help protect against rootkits, programs that are designed to hide the fact that a PC has been compromised, and is also designed to run efficiently by scanning when the PC is idle and conserving on memory usage.

If you already have antivirus software installed you probably don't need this service. Security Essentials doesn't detect if you have security software installed but does provide a message upon install that says two antivirus products aren't necessary and could interfere with each other, Packer said.

Microsoft announced in November that it was dropping its Live OneCare service in favor of a slimmed-down free offering designed to encourage more people, particularly those who don't want to pay for it and fear it will slow down their computer, to use antivirus software.

The new service lacks features like managed firewalls, performance-tuning, backup and restore, printer-sharing and multi-PC management that the OneCare service offered.

"We don't see Security Essentials as a direct competitor to other free products and suites," which try to "upsell" users, or get them to eventually pay for a product, Packer said. "We're targeting people who aren't protected" already.

A spokeswoman for AVG, likely the main rival to Microsoft's service, said AVG offers a free Internet security suite that has advantages because it is operating system agnostic and was developed by a company that specializes in security products.

Asked what Microsoft's strategy is for mobile, Packer said he couldn't comment on what the Windows Mobile team is doing.

"In general, the way we look at mobile from a security standpoint is that you are better off preventing the malware from getting on a mobile device rather than trying to run anti-malware or antivirus software," he said. "We haven't targeted mobile antivirus software because we felt that's not the right approach."

Microsoft Security Essentials will be available for download from Microsoft's Web site beginning on Tuesday.

This is what the interface will look like when the service finds that the PC is clean of malware infections.

(Credit: Microsoft)

This screenshot shows what a user will see when Security Essentials finds malware on the PC.

(Credit: Microsoft)