Hacking group LulzSec has leaked files from an Arizona police website as part of its recent wave of cyber attacks.
LulzSec said it was releasing documents that related to border control and other law enforcement activities due to its opposition to a tough anti-immigration law in Arizona.
The anonymous group of hackers posted the results of its hacks on Twitter, the microblogging site where the group has cultivated more than 240,000 followers, under the headline "Operation Chinga La Migra" - a Spanish translation for a more profane way of saying "Screw the Immigration Service".
"We are aware of computer issues," said Steve Harrison, a spokesman for the Arizona Department of Public Safety.
"We're looking into it and of course we're taking additional security safeguards."
LulzSec released about a half a gigabyte of data, including account names, passwords and contact information for several people.
Other files appeared to be security bulletins from other law enforcement agencies, internal planning documents and even routine reports on traffic incidents.
The Mexico border state passed a law last year ordering police to check the immigration status of anyone suspected to be in the United States illegally, in a bid to curb illegal immigration and border-related crime.
Critics described the law as unconstitutional and warned it could lead to the harassment of Hispanic-Americans, calling for an economic boycott of Arizona.
LulzSec's attacks on Sony, the CIA, News Corp's Fox TV and other targets have mostly resulted in temporary disruptions of some websites and the release of user credentials.
Few arrests have been made, including that of Essex teenager Ryan Cleary, 19, who was arrested this week on suspicion of being connected to attacks on the websites of Sony, the CIA and UK national police unit SOCA (Serious Organised Crime Agency).
Spanish police earlier this month also arrested three men on suspicion they helped Anonymous, a second rogue hacking group that has teamed up with LulzSec.
Hacker attacks forced Brazil to shut down its presidential website and other government sites temporarily this week, just a day after cyber attacks briefly disabled other government sites.
LulzSec, whose hacks started to hit headlines last month, has published the email addresses and passwords of thousands of alleged subscribers to porn sites.
It has used DDoS (distributed denial-of-service) attacks to temporarily take down the public website of the CIA, and it published data from internal servers of the U.S. Senate.
Security experts who have researched LulzSec's origins say it emerged from Anonymous, which became famous for attacking the companies and institutions that oppose WikiLeaks and its founder, Julian Assange.
Anonymous also attacked Sony and governments around the globe that it considered oppressive.
LulzSec's members are believed to be scattered around the world, collaborating via secret internet chat rooms.
Suspected leaders include hackers with the handles Kayla, Sabu and Topiary, security experts say.
The group's name is a combination of lulz, which is slang for laughs, and sec, which stands for security.