The FBI is probing allegations that a number of Hollywood celebrities have been hacked, after semi-naked pictures of Scarlett Johansson leaked onto the internet, the agency said.
The photos, apparently taken by the actress herself, were published on gossip websites, while there were reports also of a hacked picture of Justin Timberlake, taken by actress Mila Kunis.
"The FBI is investigating the person or groups responsible for a series of computer intrusions involving high-profile figures," said Laura Eimiller of the Federal Bureau of Investigation (FBI) office in Los Angeles.
She would not name any of the alleged victims "due to the pending nature of our investigation," but it was thought there had been a recent uptick in alleged hacking of stars, initially reported earlier in the year.
The pictures of Johansson, star of The Horse Whisperer, Lost In Translation and Girl with a Pearl Earring, showed her in a state of undress in a home setting.
In one she was holding a towel round herself with face to the camera, her unclothed rear view clearly visible in a mirror, while in the other she was topless. In the first picture she was photographing herself with a smartphone camera, and appeared to be doing so in the second, on a bed.
A publicist for Johansson did not immediately respond to a request for comment.
The TMZ website meanwhile reported that actress Mila Kunis had been hacked, and that pictures of Timberlake - with whom she starred in Friends with Benefits - had been leaked.
Two of the pictures show Timberlake, one shirtless in bed, another with a pair of pink panties on his head; another shows Kunis in a bathtub, and a fourth is explicit in nature, of an unidentified male, TMZ reported.
The FBI spokeswoman declined to say how exactly the celebrity victims may have been hacked.
"What traditionally was called computer intrusion can nowadays mean anything from..compromise of a desktop, a laptop, an iPad, a phone or really any device with which one can access personal information via the internet."