I'm at a loss to explain this unless SmartBro's DNS or proxy servers have been taken over. Here's the deal. I'm surfing normally, and then suddenly I try to go to a normal site (economist.com, yahoo.com, facebook.com, google. com, iptools.com etc) and instead of getting the correct page, I get a weird spammy advertising page, even though the URL in the Address bar looks correct.
The image to the right is an example. Click on the image to get a full sized view. I have more examples saved if anyone is interested.