The 'Find My Friends iPhone app let an American catch his cheating wife.
The new Apple app uses GPS to let designated friends 'see' where you are, showing a live location on the mobile screens.
The idea is to make it easier to find friends on a night out, or ensure that people don't get lost on holiday.
But one wronged New York husband claims that the app - which uses GPS to let designated friends 'see' where you are - has revealed that his wife was lying to him, reports the Daily Mail.
He did, however, have to activate the app on her phone without her knowledge first. The service is 'opt in', so friends have to agree to 'watch' one another.
In a post on Mac forums, the husband wrote, "I got my wife a new 4S and loaded up Find My Friends without her knowing. She told me she was at her friend's house in East Village."
"I've had suspicions about her meeting this guy who lives uptown. Lo and behold, Find my Friends has her right there."
He claimed that the app showed that she was in Manhattan, not where she claimed she was.
"I just texted her asking where she was and the dumb b***h said she was on 10th Street."
"Thank you Apple, thank you App Store, thank you all. These beautiful treasure trove of screen shots is going to play well when I meet her at the lawyer's office in a few weeks," he added.