A ring of hackers that boasted it would pry into celebrities’ phones and e-mail accounts appears to have delivered on that promise. Reported hacks of actresses Scarlett Johannson and Mila Kunis led to racy photos posted on the web.

The FBI is reportedly investigating the alleged hack involving Johansson, as well as intrusions into the phone, Twitter and e-mail accounts of some 50 other celebrities, including Vanessa Hudgens and Jessica Alba.

A group calling itself Hollywood Leaks, self-identified as an offshoot of Anonymous, boasted last month in a YouTube video that it would be targeting celebrities and the “Jew-controlled media” over the next weeks.

In the video, the hackers say:

“Attention Hollywood. We are Anonymous. We have been watching you. We have been listening to you. You have been allowed to run free too long. The time of Jew-controlled media is over. We are taking back the media with your faggot vampires and Scientology pastors. We are here for the people. We are here for the Lulz. We are here to stay. We have your lives. We have your blood, sweat and tears. Over the next couple of weeks, everyone will have them. We will rock you for ages. Consider this our acceptance speech for the Video Music Awards.”

The group claimed responsibility for leaking hacked images of rapper Kreayshawn last month. It’s not clear if the group is responsible for the leaks of information from Johansson and Kunis.

Photos that Johansson took of herself in the nude appeared online this week, as did photos showing Kunis and Justin Timberlake in intimate settings.

The photos of Johansson show her looking seductively at a phone camera as she snaps images of her bare breasts while lying on a bed. There’s also an image of her bare backside, taken as she looks into a mirror.

One of the photos of Kunis, which has not appeared online yet, show her in a bathtub, with only her head peeking above the edge of the tub, according to TMZ, which has apparently seen the images. A separate photo of Timberlake shows him lying shirtless in a bed with a pair of pink women’s underwear over his head. Another photo, which TMZ identifies only as “explicit in nature,” shows an unidentified male.

The FBI is said to be investigating the leaks. It’s unclear how the breaches occurred, though mass breaches like this generally occur after a hacker gains administrative access to an internal network where passwords are either stored in an unencrypted format or can be reset by an administrator, allowing an intruder with administrator credentials to gain access to accounts. Hacks like these have also been accomplished in the past by intruders simply accurately guessing the poor passwords and security questions celebrities set up for their accounts.

The tradition of hacking celebrities began in 2003 when a hacker named Nicolas Jacobsen breached T-Mobile and gained access to the Sidekick account of celebutant Paris Hilton’s account.

More recently, a hacker named Josh Holly, aka TrainReq, grabbed headlines in 2008 when he boasted of hacking into the Gmail account of former Disney star Miley Cyrus. He allegedly posted a series of provocative photos of Cyrus online that she had reportedly taken of herself and sent to singer Nick Jonas during the time that she dated him.

The images showed the then 15-year-old Cyrus in a wet T-shirt in the shower, baring her midriff while blowing a kiss to a mirror, and posing seductively in her underwear and bathing suit.