Hackers have struck again.

This time they've broken into a website run by the Bay Area Rapid Transit District's police union and posted online the names, postal and email addresses of officers.

It’s the latest salvo in an ongoing battle pitting hackers and activists against BART.

Today’s attack comes just two days after a staged protest shut down BART stations during a busy commute and three days after hackers broke into another BART-related site, myBART.org and exposed customer data.

The loose group of people that form notorious hacker group Anonymous took credit for that particular hack and called for the protest.

It is unclear who is behind this attack. The Twitter account @AnonOps, the closest thing the organization to an official mouthpiece, cautioned followers to "stay skeptical," claiming that the hack "could be the work sanctioned by those who truly support anonymous, or agent provocateurs."

BART Interim General Manager Sherwood Wakeman condemned the hack. “We are deeply concerned about the safety and security of our employees and their families. We stand behind them and our customers who were the subject of an earlier attack. We are deeply troubled by these actions."

The fighting began Thursday during a protest against a fatal shooting of Charles Blair Hill by BART police on July 3  in San Francisco.

BART shut off cellphone service in its downtown San Francisco stations to keep protesters from communicating. The protest itself was small. But BART’s cellphone shutdown created an uproar among cyber and civil libertarians that has not yet gone away.

The ACLU has condemned the shutdown. And the Federal Communications Commission also is investigating, according to press reports.

Anonymous has called for another BART protest on Monday.

Photo by Steve Rhodes