Anonymous computer hackers broke into a BART website and revealed personal information on thousands of BART riders Sunday; part of a protest that could include a disruption of train service during the Monday afternoon commute.

Transit officials closed down the myBART website, which is run by an external vendor, and urged anyone who subscribed to the news alert service to change their passwords on other websites if they use the same password they used for myBART.

The anti-BART hackers, angered at the agency’s tactics to curtail previous protests, posted the names, street addresses, email addresses, phone numbers and passwords of at least 2,400 of the website’s 55,000 email subscribers on a website, www.djmash.at/release/users.html.

“I think that’s completely inappropriate,” said Livermore resident Annamarie Hastings, one of the people whose information was posted online. “It doesn’t make me any more sympathetic to their cause.”

Hastings said she had signed up for the myBART news alerts years ago to get important information about her commute to work. She said she was angered at the protesters, not BART, for exposing her personal information.

As it battled attacks on its websites and tried to inform thousands of customers about the breach, BART officials also worked to thwart plans by protesters to disrupt the Monday afternoon commute at the Civic Center station in downtown San Francisco.

“We’re making preparations to try to prevent any unsafe conditions on the platform,” said BART spokesman Jim Allison. “I’m not going to discuss any specifics, other than to say we’re preparing.”

In a video manifesto posted Sunday, an international computer hacking group that calls itself Anonymous or AnonyOps instructed Bay Area residents to wear red shirts, masks and bring cameras to a planned protest at 5 p.m. Monday.

The original protests faulted BART police for the fatal shooting of a homeless man last month, but now encompass larger free speech issues after BART shut down cellphone communications in its trains and stations during a protest on Thursday.

“You have angered Anonymous,” said the video message, which was directed at BART. A computerized voice relayed the two-minute message backed by a dramatic musical soundtrack.

The group also instructed protesters to inundate the work and personal email inboxes of several dozen officials from BART and other agencies.

“This is a Black fax and email Bomb action, the goal being to explode their inboxes,” the website said. And the hackers also broke into the website of a police anti-DUI website, California Avoid, and superimposed a masquerade mask over the face of a highway patrol officer.

BART has not ruled out shutting down cell phone communications again Monday.

“It’s certainly a double-edged sword,” said Joel Keller, a Brentwood member of the BART’s board of directors.

“We do inconvenience our riders and potentially present some problems for them. At the same time, if we disrupt communication for people who are trying to create problems for the district, it may ensure our riders have a smoother commute.”

Keller said he is sympathetic to those concerned that the tactic violates rights to freely communicate, but he said law enforcement must be able to stop people from disrupting train service.

Allison said the agency has places where people can protest outside the station, but not on the platform and inside the trains.

“We fully welcome people who have different views and opinions, and we have a place to do that, but the platform is a place for people to get on and off trains,” Allison said.

BART board member Gail Murray, of Walnut Creek, said allowing protests inside the station can threaten the lives of passengers. She defended the tactics BART has used and countered allegations that the BART maneuvers resembled those by dictators seeking to suppress dissent.

“It’s a touchy thing because all of the Middle East, the Arab Spring, makes it look, I think, more authoritarian than was the intent,” Murray said. “The intent by our police was definitely to protect our passengers. It was shown from the previous protest that it was extremely dangerous, all those people pushing and shoving.”

The anonymous group said its Monday protest would be peaceful and offered a partial apology to the thousands of people whose personal information it exposed online.

“We apologize to any citizen that has his information published, but you should go to BART and ask them why your information wasn’t secure with them,” the hackers wrote.

“Also do not worry, probably the only information that will be abused from this database is that of BART employees.”