The episode occurred on Saturday, and lasted for approximately 40 minutes, when users were warned that all sites listed by the search engine “may harm your computer”.

In the official Google blog, Marissa Mayer, vice president for search products and user experience, wrote that the cause was “very simply, human error”.

“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. Fortunately, our on-call site reliability team found the problem quickly and reverted the file.”

Google regularly works with stopbadware.org, a nonprofit project headed by legal scholars at Harvard and Oxford universities, who investigate consumer complaints, in its efforts to determine which sites might install malware onto a user’s computer.

"We will carefully investigate this incident and put more robust file checks in place to prevent it from happening again," assured Mayer.