From CNN:

Microsoft Corp., whose popular Windows software is a frequent target for Internet viruses, is offering a free security program to remove the most dangerous infections from computers.

The program, with monthly updates, is a step toward plans by Microsoft to sell full-blown antivirus software later this year.

Microsoft said Thursday that consumers can download the new security program from the company's Web site www.microsoft.com and that updated versions will be offered automatically and free each month.

It will be available starting Tuesday.

Full article here.