A man pleaded guilty on Monday to hacking into the email accounts of such celebrities as Christina Aguilera, Mila Kunis and Scarlett Johansson, whose nude photos eventually landed on the Internet.

Christopher Chaney, 35, entered his plea in federal court to nine counts, including unauthorized access to a computer and wiretapping. He was immediately taken into custody. Sentencing was scheduled for July 23.

Chaney was arrested in October as part of a yearlong investigation of celebrity hacking that authorities dubbed "Operation Hackerazzi."

Prosecutors said Chaney illegally accessed the email accounts of more than 50 people in the entertainment industry.

Nude photos Johansson had taken of herself were later posted on the Internet. Aguilera also had private photos put online, court documents show.

Johansson told Vanity Fair for its December issue that the photos were meant for Ryan Reynolds, now her ex-husband.

Chaney mined through publicly available data to figure out password and security questions for celebrity accounts. He also hijacked a forwarding feature so a copy of every email a celebrity received was sent to an account he controlled, according to court documents.

A search warrant unsealed and obtained by The Associated Press said Chaney's computer hard drive contained numerous private celebrity photos and a document that compiled their extensive personal data.

Chaney forwarded many of the photographs to two gossip websites and another hacker, but there wasn't any evidence that he profited from his scheme, authorities said. He has since apologized for his actions.