CNET reports that 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 will be free and remain free even after the beta period is over.

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.