Yahoo and McAfee have joined forces to warn users of potentially dangerous Web sites along side results generated at Yahoo.com

The new feature will start on Tuesday and couldn’t be easier to understand. After a completed search query users will see a red exclamation point and a warning next to the link that McAfee have found to contain dangerous downloads or using visitors e-mail addresses to send out spam. Yahoo and McAfee hope the move will stop users worrying about clicking a malicious link.

Director of product management for Yahoo’s search division Priyank Garg said, “Yahoo users have clearly told us that among the most important concerns for them are all these lurking threats on the Internet… They know the damage they can do but they don’t know how to protect themselves.”

If McAfee identifies a site as one that tries to automatically install malicious code on visitor’s computers or attempt “drive-by downloads”, Yahoo users won’t see the link at all.

“When a user gets a set of search results, there’s really no indication of who’s a good guy and who’s a bad guy,” said Tim Dowling, vice president of McAfee’s Web Security Group. “You’re really leaping off a platform of faith that you’re clicking on a site that’s safe and not one that’s bad. And the bad guys really try hard to look good.”

The technology being used on Yahoo’s site is a stripped-down version of McAfee’s full SiteAdvisor technology which is free directly from McAfee. It uses red, yellow and green icons to label safe and harmful sites. A premium version adds other features.

Yahoo’s Garg said the company was doing experiments to identify malicious sites and bar them from search results.

But he said “security is not Yahoo’s forte” and McAfee’s technology gives Yahoo the breadth and depth “many orders of magnitude greater than what we had before.”

Yahoo is the worlds second most popular search engine among U.S. users with a 21 percent share of the market with Google holding 60 percent.