Google works with a nonprofit organization that runs the site StopBadware.org to obtain a list of URLs that are known to install malicious software if users go to those sites. StopBadware researches complaints regarding sites and decides which URLs should be on the warning list, so "since each case needs to be individually researched, this list is maintained by humans, not algorithms," according to an official Google blog post Saturday morning credited to Marissa Mayer, the company's vice president of Search Products & User Experience.

Google "periodically" gets updates to the URL warning list and got such an update for release on its site Saturday morning. "Unfortunately (and here's the human error), the URL of '/' was mistakenly checked as a value to the file and '/' expands to all URLs," she wrote. "Fortunately, our on-call site reliability team found the problem quickly and reverted the file."

Mayer apologized in her post to anyone who was inconvenienced by the glitch and to site owners whose pages were incorrectly labeled as being malicious. "We will carefully investigate this incident and put more robust file checks in place to prevent it from happening again," she wrote.may be harmful to your computer."

StopBadware operates as a partnership among academic institutions, IT companies and volunteers, according to its site. It is operated out of Harvard Law School's Berkman Center for Internet & Society.