"This is a flagrant violation of privacy. The authorities have been contacted and will prosecute anyone who posts the stolen photos of Jennifer Lawrence," spokeswoman Liz Mahoney said in an emailed statement. She did not say who was contacted.
A spokesman for the FBI said the agency "is aware of the allegations concerning computer intrusions and the unlawful release of material involving high profile individuals, and is addressing the matter."
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Model Kate Upton was among celebrities whose photos were posted online. Her lawyer, Lawrence Shire, called them "an outrageous violation" of her privacy.
"We intend to pursue anyone disseminating or duplicating these illegally obtained images to the fullest extent possible," he said in a statement.
The photos were posted on the image-sharing forum 4chan. Britain's Mirror website quoted the anonymous uploader as saying on the site he or she was a collector, not the hacker.
The uploader said the photos had generated $120 in bitcoin, a digital currency, but added: "I really didn't get close to what I was hoping."
After reports that the photos had apparently come from hacked iCloud accounts, Apple launched an investigation and found that a targeted attack on celebrity accounts' security information had caused the leak, rather than a systems breach on iCloud or Find my iPhone.
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Actress Mary Elizabeth Winstead said on Twitter that nude photos of her were also posted online. She said the photos had long been deleted.