McAfee has agreed to buy SiteAdvisor, a Web-site rating company that tests sites to see if they install spyware and viruses.

Founded by a group of Massachusetts Institute of Technology engineers in April 2005, SiteAdvisor attracted attention from the public - and McAfee - when it released a free browser toolbar designed to warn users of risky Web sites, last month.

McAfee will continue to offer the free SiteAdvisor toolbar, which superimposes its own Web-site ratings on top of search results from sites such as Google and Yahoo, said Bill Kerrigan, executive vice president of McAfee's consumer group.

The company will extend the technology with a new line of "safe search" products, the first of which is expected this year. "I see it emerging as a new category," said Kerrigan. The products "would give a consumer more information relative to [his or her] search results," and could help users avoid inappropriate sites and dodge spyware, .

SiteAdvisor's database of 2.7 million Web pages may play into future enterprise offerings, but McAfee will most likely start with a stand-alone consumer product, Kerrigan said.

McAfee will boost the SiteAdvisor user base and speed up the company's software development, said SiteAdvisor's chief executive officer Chris Dixon in a posting to the company's Web site. It will also allow SiteAdvisor to "leverage both McAfee’s world class security technology and leading research capabilities to bring additional layers of protection to SiteAdvisor’s already extensive safety database," he added.

SiteAdvisor employs a staff of "less than 25," said Kerrigan, who would not reveal the terms of the acquisition.