Microsoft is buying anti-virus/anti-spam company Sybari Software in an undisclosed deal.

It will use the acquisition to add to its business security software, the company said. The acquisition is Microsoft's first in the anti-virus market since the company purchased technology from Romanian company GeCAD in June 2003. It also comes amid speculation that Bill Gates will use a keynote speech at next week's RSA Security Conference to announce plans for a new consumer anti-virus product.

New York-based private company Sybari makes anti-virus, anti-spam and e-mail content filtering products for big companies. Its Antigen anti-virus product is server-based and uses several anti-virus engines to scan e-mails.

Microsoft was prompted into the purchase by customer demand for more anti-virus protection on Exchange servers, said Microsoft security VP Mike Nash. Sybari gives customers a choice of anti-virus engines from Sophos, CA and Kaspersky, but the company does not have its own engine. Sybari works with Microsoft Exchange e-mail server, as well as Microsoft Office SharePoint Portal Server 2003 and Microsoft Windows SharePoint Services.

The purchase is not surprising, considering Sybari's strength on Microsoft Exchange and the two companies' close business ties, said IDC analyst Brian Burke. In fact, Microsoft commonly recommended Sybari to customers looking for an anti-virus product that works with Exchange, Burke said.

Sybari's use of other companies' engines also stays true to Microsoft promises to avoid domination of the anti-virus software market and play fair with competitors. In a statement, Microsoft said it would continue to support multiple versions of Sybari's software for Exchange and Lotus Notes.

However, Microsoft said that it does plan to add its own anti-virus engine, which it acquired from GeCAD, to the list of those that run on Antigen. That could spell trouble for Sybari's anti-virus engine partners, Burke said.

Nash said that internally, Microsoft has already been using the GeCAD engine, now referred to as the "Microsoft anti-virus engine", with the Sybari technology.

Sybari's Chief Executive Officer Robert Wallace said, in a statement, that he welcomed the addition of Microsoft's expertise and the opportunity to offer Sybari technology to more businesses.

Microsoft has been adding to its stable of security software in recent months. In December, the company announced it was buying Giant Company Software. The company later released a free test version of Giant's product, Giant Antispyware, under the name Microsoft Antispyware.