LOS ANGELES -- In a major breach of privacy, a hacker leaked a series of pictures allegedly showing Jennifer Lawrence and other female celebrities in the nude.
Federal investigators are looking at the hacking, according to the FBI's Los Angeles office.
"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," FBI spokeswoman Laura Eimiller said Monday. "Any further comment would be inappropriate at this time."
Apple confirmed Monday that it is looking into reports that its popular iCloud online data backup service may have been compromised by the hackers.
"We take user privacy very seriously and are actively investigating this report," Apple spokeswoman Natalie Kerris said.
Purported nude photographs of Lawrence, who stars in "The Hunger Games" series and won an Academy Award last year for her role in "Silver Linings Playbook," were splashed on various sites Sunday. They appeared on 4chan, Reddit, Twitter and Tumblr, among others.
Celebrity blogger Perez Hilton followed suit, and posted what he said were naked photos of Lawrence and actress Victoria Justice.
He later took them down.
"Upon further reflection and just sitting with my actions, I don't feel comfortable even keeping the censored photos up. I am removing them," Hilton tweeted. "At work we often have to make quick decisions. I made a really bad one today."
The leaked photos sparked an online backlash, with some of the targeted celebrities decrying them as fake while others confirmed they're real.
Lawrence's publicist said the photos are a "flagrant violation of privacy."
"The authorities have been contacted and will prosecute anyone who posts the stolen photos of Jennifer Lawrence," the publicist said.
Other celebrities targeted also spoke.
"To those of you looking at photos I took with my husband years ago in the privacy of our home, hope you feel great about yourselves," actress Mary E. Winstead wrote.
"Knowing those photos were deleted long ago, I can only imagine the creepy effort that went into this. Feeling for everyone who got hacked."
Some celebrities said the photos were doctored.
Photos claiming to show Ariana Grande are "completely fake," someone close to the singer said. Justice said pictures purporting to be of her are not real, either.
Hacking of celebrity accounts has become more popular in recent years.
Two years ago, a judge sentenced Christopher Chaney of Florida to 10 years in federal prison for stealing nude photos, scripts and personal information from the e-mail accounts of 50 entertainment industry figures. The celebrities involved included movie stars Scarlett Johansson and Mila Kunis and singer Christina Aguilera.
The first real case of a celebrity hacking was in 2005. Hackers logged into Paris Hilton's phone and stole photos of the reality star, said Mikko Hypponen, chief research officer at computer security company F-Secure, in 2011.
At the time, the hackers broke into Hilton's phone by guessing the not-so-secret answer to her security question, which was "tinkerbell" -- the name of her pet Chihuahua.