Not very long ago I went to a website that I had been too many times and was instantly under attack from rogue code that had been planted onto the site. Yep, it had been hacked.
In that situation, shut down your browser as soon as possible, then do a full virus and malware scan of your computer before you do anything else. I use Zonealarm Extreme Security on all my computers and it does a good job of blocking virus and malware attacks from websites, Internet worms, and email. It also has a junk mail filter that works really well included. As a backup, I also use Malwarebytes Anti-Malware from malwarebytes.org. The free version works great and will find most things that a lot of other programs may miss.
After you’ve cleaned up your system, you should always report the site to at least Google so that others don’t stumble upon the website and get infected as well. You can report hacked websites to Google here.
Another great site to report hacked websites to is badwarebusters.org. They act as a repository for sites like this and notify other companies and sites via regular updates.