<A target="_blank" href="http://www.zdnet.com/blog/bott/microsoft-calls-out-firefox-and-chrome-for-security-weaknesses/4070">If you visit Microsoft's site, called Your Browser Matters, it will check your browser</A> for security weaknesses. Well, some browsers. IE 9, predictably, gets a top score. If you dig deep enough, you can get an explanation of the rating system.