PHOENIX (Reuters) - Computer hackers who previously broke into a U.S. Senate server and brought down the CIA web site struck an Arizona police web site on Thursday, releasing dozens of internal documents over the Internet.

Lulz Security, saying it opposed a tough anti-immigration law in Arizona, said it was releasing documents that related to border control and other law enforcement activities. Its headline was "Chinga La Migra," Spanish for a more profane way of saying "Screw the Immigration Service."

It released about a half a gigabyte of data, including account names, passwords and contact information for several people. Reuters was able to reach two of them to establish that they were accurate.

A scan of the dozens of files released revealed what appeared to be security bulletins from other law enforcement agencies, internal planning documents and even routine reports on traffic incidents.

"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."

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.

A majority of Americans supported the measure, but outraged opponents charged it was unconstitutional and would lead to the harassment of Hispanic-Americans, and called for an economic boycott of the desert state.

The most controversial parts of the law were blocked by a federal judge shortly before it came into effect last July, although Arizona is pursuing an appeal.

Few arrests

Lulz, a group of rogue hackers who have not been identified, posts the results of its hacks on Twitter, the microblogging site where the group has cultivated more than 240,000 followers.

So far LulzSec's publicized assaults on Sony Corp., 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.

There have been few arrests in the hacks. British police said Tuesday that they had arrested a 19-year-old man on suspicion that he was connected to attacks on Sony, the CIA and a British police unit that fights organized crime.

Spanish police earlier this month apprehended 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 Thursday, 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 temporarily took 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.