Nick Bilton for The New York Times:

Girls Around Me uses Foursquare, the location-based mobile service, to determine your location. It then scans for women in the area who have recently checked-in on the service. Once you identify a woman you’d like to talk to, one that inevitably has no idea you’re snooping on her, you can connect to her through Facebook, see her full name, profile photos and send her a message.

C.R.E.E.P.Y.