The Mountain View, Calif. company apologized for any inconvenience and blamed the mistake on human error, according to Marissa Mayer, VP, search products and user experience.

The problem began at 6:30 a.m. PST and ended at approximately 7:25 a.m. PST. Those who did a Google search during that hour saw the message.

Google said that the problem occurred because a Google employee accidentally typed "/" for the whole URL of a bad Web site in the database of harmful sites. The glitch was quickly caught and fixed by on-call staff.

Google flags search results with the message if the site is known to install malicious software in the background or otherwise surreptitiously to protect users against visiting sites that could harm their computers. The company said it maintains a list of sites based on criteria developed by a company called StopBadware.org, a nonprofit project headed by scholars at Harvard and Oxford universities.

"Despite today's glitch, we continue to support Google's effort to proactively warn users of badware sites, and our experience is that they are committed to doing so as accurately and as fairly as possible," StopBadware.org team lead Maxim Weinstein wrote in a blog post.

This news story is important. I recommend that everyone read it.