Google has reported an internet user to police after spotting images of child abuse in the man's Gmail account.
Police in the US city of Houston arrested the man after a child protection agency was tipped off by the search engine giant.
Gmail - the company's email service - is used by about 400 million people worldwide.
Google has already notified users that it can scan their messages to help provide "personally relevant" advertising.
This capability puts the company one step ahead of law enforcement in this area, with Detective David Nettles saying: "I can't see that information, I can't see that photo, but Google can."