The American hacker who illegally accessed email messages of Hollywood celebrities apologised to his victims, who included Scarlett Johansson, Mila Kunis and Christina Aguilera.

"I deeply apologize. I know what I did was probably one of the worst invasions of privacy someone could experience," Christopher Chaney declared over CNN affiliate WAWS/WTEV in Jacksonville, Florida on Wednesday, according to CNN.

Chaney, who was arrested in his home in Jacksonville, Fla. on Wednesday, has been charged by the FBI for unauthorised access of protected computers, damage to protected computers, wiretapping and aggravated identity theft. Out on a $10,000 bond, he faces a 121-year sentence if convicted.

FBI investigators targeting hackers of celebrities' email accounts found that Chaney victimised 50 celebrities. He hacked their email passwords with clues from social media and online sites used by his victims. Once he accessed the email account, he then set it to forward copies of emails to his email account, and to continue receiving emails even if the victims reset the passwords of their email accounts.

Chaney also learned the email addresses of other celebrities by getting them from the contact list of his victims. He also hacked their email accounts.

Chaney was able to steal nude photos of his victims and posted these online. The FBI is investigating if nude photos of Scarlett Johansson spreading online came from Chaney.

Chaney claimed he got addicted to hacking celebrities' email accounts and did not know how to stop until FBI agents confiscated his computers.