If you did a Google Internet search between 9:30 a.m. ET and 10:25 a.m. ET on Saturday, 31 Jan 2009, you likely were unable to access any website in the search results list becouse Google labelled all url’s, as a malicious website with the warning “This site may harm your computer.”

Google labelled all websites, even www.google.ca, as a malicious website with the warning “This site may harm your computer.”

Clicking the warning took the user to a page which explained that “This warning message appears with search results we’ve identified as sites that may install malicious software on your computer.”

Google later said the problem occurred because of “human error” and issued an apology.

Google flags search results with a warning message if a site is known to install malicious software in the background or otherwise surreptitiously.
During a routine update to a list of so-called badware sites, Google said a symbol was un-checked (off) by mistake that expanded the warning to all URL’S.

(google news)