What happened? Very simply, human error. Google flags search results with the message “This site may harm your computer” if the site is known to install malicious software in the background or otherwise surreptitiously. We do this to protect our users against visiting sites that could harm their computers. We work with a non-profit called StopBadware.org to get our list of URLs. Since each case needs to be individually researched, this list is maintained by humans, not algorithms.

We periodically receive updates to that list and received one such update to release on the site this morning. Unfortunately (and here’s the human error), the URL of ‘/’ was mistakenly checked in as a value to the file and ‘/’ expands to all URLs.

http://googleblog.blogspot.com/2009/01/this-site-may-harm-your-computer-on.html