Lot's of secure servers will recognize when you try to log in from an IP address or particular browser/machine combination you haven't used before. My bank did that to me last year when I started using FireFox and again every time I update a browser, OS, or VPN connection I have to answer security questions. So far they have been the security questions I typically use. If I see one I don't know I exit the browser and then open it and try to log in again. Doing so usually generates a different question.
What I've noticed with IE8 is that many secure websites come up blank so you have to use the compatibility view to use them. That really sucks, especially if you don't know how to turn on compatibility view because the browser doesn't suggest it. It just displays a blank page with the correct URL like the website is broken or something.