Official Google Blog: "This site may harm your computer" on every search result?!?!
http://googleblog.blogspot.com/2009/01/this-site-may-harm-your-computer-on.html

If you did a Google search between 6:30 a.m. PST and 7:25 a.m. PST this morning, you likely saw that the message "This site may harm your computer" accompanied each and every search result. This was clearly an error, and we are very sorry for the inconvenience caused to our users.

Well that explains that...

"If you did a Google search between 6:30 a.m. PST and 7:25 a.m. PST this morning, you likely saw that the message "This site may harm your computer" accompanied each and every search result. This was clearly an error, and we are very sorry for the inconvenience caused to our users. What happened? Very simply, human error" bit worrying really