FBI Closing in on Hackers That Stole Nude Scarlett Johansson Photos

TMZ broke the story ... Scarlett contacted the FBI yesterday after the pics -- one which features her bare breasts and another showcasing her behind -- were leaked to several websites.

Law enforcement sources tell TMZ ... the FBI is "honing in" on the group of hackers and know the identity of at least one of them -- and we're told it's the ringleader.