As widely expected, Microsoft ( MSFT) announced plans Thursday to offer a security product to help business customers protect computers from spyware, viruses and other attacks, stepping up competition against Symantec ( SYMC) and McAfee ( MFE).

Microsoft, which already has announced plans for a security product for consumers, said Thursday that an early beta version of its business offering will be available by the end of the year. The software giant will announce pricing and licensing for the product, called Microsoft Client Protection, at a later date.

Microsoft also announced plans to release antispam and antivirus software called Microsoft Antigen for messaging and collaboration servers based on technology from recently acquired Sybari Software. Microsoft Antigen for Exchange is scheduled to be available in beta form to customers in the first half of 2006.

The Microsoft security products for business customers come just a few months after Microsoft unveiled a consumer product called Windows OneCare that will provide automatically updated antivirus, antispyware and firewall protection. OneCare is expected to be available around the end of the year.

With both consumer and business security products, Microsoft is stepping into the turf previously dominated by such companies as Symantec, McAfee, Computer Associates ( CA)and Tokyo-based Trend Micro ( TMIC).

Shares of Microsoft recently inched up 8 cents to $24.75, while shares of Symantec fell 39 cents, or 1.7%, to $22.20. McAfee was down 37 cents, or 1.2%, at $30.74, while Trend Micro was up 19 cents, or 0.6%, at $32.39.

While Microsoft is likely to enjoy some success with its consumer security products, many analysts and investors believe businesses, particularly large enterprises, will be reluctant to allow Microsoft to protect their systems. Enterprises, they have suggested, are likely to prefer an outside vendor for security because it's often weaknesses in Microsoft's software that permit attacks in the first place.