The Anonymous hacking group has taken another swipe at police in Arizona, launching online attacks against several police union websites and publishing email messages stolen from law enforcement officers.

Regional sites belonging to the Fraternal Order of Police were defaced Thursday night and many of them remained offline Friday. Anonymous took credit for the attacks, saying it was continuing its assault in protest of the state's tough anti-immigration laws.

Anonymous said it had defaced eight Fraternal Order of Police (FOP) websites and was releasing a list of more than 1,200 police usernames, passwords and email addresses. It encouraged other hackers to search through "everybody's inbox to retrieve and expose their secrets".

It also published personal email messages of several FOP members containing passwords, credit card numbers and, in some cases, anti-immigrant chain messages. Representatives from the affected Fraternal Order of Police organisations did not reply to messages seeking comment Friday.

Anonymous, along with another now-disbanded hacking group, LulzSec, has been running an ongoing "Antisec" attack against government, law enforcement and corporations for weeks now. In two separate incidents, it has previously released messages belonging to the Arizona Department of Public Safety and other police data.

The Arizona Department of Public Safety has called the hackers a "cyber terrorism group."