 -- The FBI said it is "aware" that someone has leaked nude photos purporting to be pictures of dozens of A-list celebrities including Jennifer Lawrence and Kate Upton and is "addressing the matter."

The feds made its statement as celebrities were outraged over the hacked photos.

The statements came in response to the release of photos purportedly of dozens of celebrities in various states of undress. The photos first appeared on an image sharing site called 4chan.

It's not clear how the photos were obtained or whether they are all genuine.

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"This is a flagrant violation of privacy," a spokesperson for Lawrence told ABC News. "The authorities have been contacted and will prosecute anyone who posts the stolen photos of Jennifer Lawrence."

Upton's attorney, Lawrence Shire, echoed those sentiments.

"This is obviously an outrageous violation of our client, Kate Upton's, privacy," he said. "We intend to pursue anyone disseminating or duplicating these illegally obtained images to the fullest extent possible."

The FBI issued a statement Monday saying, "The FBI is aware of the allegations concerning computer intrusions and the unlawful release of material involving high profile individuals, and is addressing the matter. Any further comment would be inappropriate at this time."

It's not clear how the photos were leaked, but Apple released a statement saying it is investigating whether any of its systems were compromised.

"We take user privacy very seriously and are actively investigating this report," the statement said.

Meantime, a representative for Ariana Grande called her allegedly leaked photos "completely fake."

Singer Victoria Justice and Olympic gymnast McKayla Maroney did the same via Twitter.

Actress Mary Elizabeth Winstead took to Twitter to indicate that the photos of her wer real, saying she had previously deleted the photos.

"Even if you have deleted those photos from your phone, often times they've already been uploaded into the cloud," said Clifford Neuman, the director of the USC Center for Computer System Security. "When you deleted them from the phone, they continue to exist."

Representatives for other celebrities who allegedly were hacked didn't immediately return calls for comment.

Hacking of celebrities' personal accounts has happened before. In 2012, a Florida man was sentenced to 10 years in prison after he pleaded guilty to hacking into email accounts and stealing compromising photos of celebrities, including Scarlet Johansson, Mila Kunis and Christina Aguilera.