McAfee Inc. on Monday launched a paid version of its SiteAdvisor Web site warning tool that checks links inserted in e-mail and instant messages and automatically blocks access to risky sites.

Dubbed SiteAdvisor Plus, the premium edition includes a link checker that places the service's URL ratings beside links in e-mail messages and instant messages. On the e-mail front, the checker supports Gmail, Microsoft Live Mail, Outlook, Outlook Express, and Yahoo Mail. It also supports Google Talk, Windows Live Messenger, and Yahoo Messenger on IM. Support for AOL Instant Messenger and AOL Mail is under development, said McAfee.

Other features include Protected Mode, which automatically blocks access to questionable sites by redirecting users to a safe page anytime the browser is pointed to a URL tagged as red or yellow by SiteAdvisor. The mode grays out sites SiteAdvisor pegs as threatening to make it clear to users which addresses are safe to surf. The service also adds phishing protection via a database of fraudulent sites updated in real time.

McAfee pitched the new offering as an add-on to its existing security suites, and as an upgrade for those using the free SiteAdvisor. "We think it's a very natural evolution that extends the core of the service," says Kelly Ford, director of marketing for SiteAdvisor. "We didn't just throw in a lot of bells and whistles."

In August, McAfee added the free version of SiteAdvisor to its consumer security suite products. There are no plans "for the foreseeable future" to toss in SiteAdvisor Plus for free. "The functionality is unique enough that we think users will pay for it," says Ford.

SiteAdvisor Plus, which costs $24.99 ($49.99 for a three-computer license), requires Internet Explorer. A version for Firefox will be released later, said McAfee. A 30-day free trial edition is available immediately from here.

McAfee's site will also offer the trial for downloading late Monday or early Tuesday.