A screen grab of a Google search for "Google glitch" made today. (CBC)

Google has apologized for a glitch that blocked people from using the search engine for a short time Saturday and warned that websites they wished to visit might harm their computers.

A company official said "each and every search result" from between 9:30 a.m. and 10:25 a.m. ET "likely resulted' in the message, "This site may harm your computer."

Marissa Mayer, vice-president of search products and user experience, writing in a Google blog, blamed the problem on human error.

She said Google flags search results with the warning if the site is known to install malicious software "in the background or otherwise surreptitiously."

However, the message appeared even for well-known, trusted sites because of an error in a list of web addresses compiled by a non-profit group that works with Google to protect users against visiting sites that could harm their computers, she said.

"This was clearly an error, and we are very sorry for the inconvenience caused to our users," Mayer said.

Users of Facebook in Canada, for instance, were advised to bypass Google and type in the address of the social networking site themselves.

"You can continue to http://www.facebook.com/ at your own risk," said the message, identified as a Google advisory.

The warning also told internet users to click on a link to give them more information on malware, a catch-all term for malicious software such as computer viruses and spyware.

"Clicking on the link to explain why Google feels this way about the site brings up a server error [message]," wrote David M. Williams on the Australian computer technology website itwire.com.

"As I write this, Google is reporting every search result as being harmful," he said. Williams said the sites to which Google would not take him included test.com and a number of pages on news.com.