Christopher Chaney, 35, pleaded guilty to nine felony counts in federal court, including wiretapping, unauthorized access to a protected computer and damaging a protected computer. The prosecution dropped a charge of aggravated identity theft in exchange for the guilty plea.
It was also revealed in court that Chaney had a prior mail fraud conviction.
Chaney admitted that he hacked into the email accounts of more than 50 people in the entertainment industry including Christina Aguilera, Mila Kunis and Scarlett Johansson.
Numerous private celebrity photos were found on Chaney's computer hard drive, along with a document that compiled extensive personal data on those celebrities. In Johansson's case, nude photos of her were obtained then posted on the Internet.
Chaney admitted he used publicly available information to figure out passwords and answers to security questions to celebrities' accounts. He then hacked into the email accounts, went through contact lists to find accounts of fellow stars, and hijacked a forwarding feature so a copy of every email a celebrity received was sent to an account he controlled, according to court documents.
He was arrested in October as part of a yearlong investigation of celebrity hacking that authorities dubbed "Operation Hackerazzi."
Chaney has since apologized for his actions. Authorities said there was no evidence he profited from the scheme.
He faces a maximum of 60 years in prison. Under a plea bargain, he also could pay a fine of up to $2.2 million and must pay restitution to his victims, ranging from $15,000 to $400,000. His sentencing was scheduled for July 23.
The Associated Press contributed to this report.