James Martin/CNET

Hackers have broken into a second Web site affiliated with the San Francisco Bay Area subway system, which has come under fire in the last week for turning off cell phone service before a planned protest.

A database belonging to the BART Police Officers Association was posted online today, complete with full names, e-mail addresses, home addresses, and passwords. BART stands for Bay Area Rapid Transit.

It was not immediately clear who was responsible for the embarrassing information leak--a Twitter account affiliated with Anonymous said that no one has "claimed responsibility for the hack," and speculated that it could be the work of either an ally or an adversary.

As of this afternoon, the BARTpoa.com Web site was offline. "These people are criminals and we're going to forward this information to the FBI," the BART union president, Jesse Sekhon, told the San Francisco Chronicle today. "These people need to be brought to justice. They can't be terrorizing people."

(Worth noting is the use of passwords that fail to meet general guidelines for creating strong passwords, such as: cowgirl, firefly, 69square, hawaii50, grover, jennifer, sfgiants, cowboytough, and BUFFY10.)

The intrusion follows a similar one on Sunday, when the amorphous Anonymous collective broke into the MyBART Web site, which allowed users to create accounts to receive discounts or special offers.

BART pulled the plug on cell service last Thursday in four subway stations in downtown San Francisco before a planned protest that was intended to call attention to the fatal shooting of an apparently homeless man named Charles Blair Hill.

Thursday's planned protest might have gone unnoticed outside the San Francisco metro area. But disabling underground cell service -- a move more associated with authoritarian regimes in the Middle East than supposedly progressive California cities -- captured the attention of Internet users around the country concerned with government overreach and civil liberties.

The Anonymous group of online activists began promoting what became known as "Operation BART," with one account announcing: "We are going to show BART (@SFBART) how to prevent a riot #OpBART." And the Federal Communications Commission said it was reviewing the legality of BART's move.

A second protest happened on Monday, prompting BART to close at least four San Francisco subway stations during the evening rush hour.

The ACLU of Northern California said in a blog post last week that: "Shutting down access to mobile phones is the wrong response to political protests, whether it's halfway around the world or right here in San Francisco. You have the right to speak out. Both the California Constitution and the First Amendment to the United States Constitution protect your right to free expression."

An archived version of the BARTpoa.com Web site says the union boasts about 230 members. Its purpose is to "enhance wages, benefits and working conditions" of BART police officers.