The hacker group Anonymous called for a protest against an earlier cellphone shutdown has succeed in temporarily closing down four San Francisco underground rail stations that was operated by Bay Area Rapid Transit (BART).

The BART commuter train service shutdown wireless networks in some stations last Thursday for about three hours to thwart demonstrators organising a protest over a police shooting of an alleged knife-wielding passenger last month.

The shutdown of the mobile phone networks on Thursday has affected about 350,000 commuters, who used to travel by BART train service. But outside the BART stations, cell phone service was not interrupted.

However, on Monday, BART agencies refrained from shutting down the wireless services, unlike last Thursday. BART officials have said their primary concern is to ensure safety.

In addition, numerous BART Police officers and other BART personnel with radios were present during the planned protest, and train intercoms and white courtesy telephones remained available for customers seeking assistance or reporting suspicious activity.

BART considered the protest as a civil disturbance during commute times at busy downtown San Francisco stations that could lead to platform overcrowding and unsafe conditions for BART customers, employees and demonstrators.

BART officials told The AP that the decision to cut cell phone service on Thursday, a moved criticized by the American Civil Liberties Union and others, was made out of concern for passengers' safety.

"It's wrong," said ACLU lawyer Michael Risher, whose group was scheduled to meet later Monday with BART's police chief at the agency's headquarters in Oakland. "There were better alternatives to ensure the public's safety."

Around 5 pm Monday, an estimated 50 protesters gathered at the UN Plaza near the Civic Center BART and Muni station, hiding their identity behind Guy Fawkes masks.

Finding itself in the midst of enraged protesters shouting “no justice, no peace,” BART shut down four of its San Francisco subway stations. Protesters reportedly stopped a Bay Area Rapid Transit, or BART, train, forcing the authorities to clear the platform for safety concerns.

"Once the platform becomes unsafe, we can't jeopardize the safety of patrons and employees," BART Deputy Police Chief Dan Hartwig told the Los Angeles Times.

They began marching northeast on Market Street towards Powell station, when San Francisco Police Department and BART police officers emerged from Civic Center station to inform public about the station's shutdown for safety reasons.

BART has informed passengers about the disruption by protesters on Sunday itself. The action was preceded by the hacking of one of BART’s Web sites, leaking data of more than 2,000 users. BART's online services including web, mobile web, email and SMS are used by nearly 2 million customers every month.

"We’re disappointed to announce that the BART website may be subject to an online attack Sunday August 14, between noon and 6 pm, because this action will directly affect those customers who depend upon our site, as well as the developers who use BART's open data services to serve BART customers," BART said in a statement.

Followed by this during mid-Sunday, BART announced that account information was compromised in connection with an illegal and unauthorized intrusion into the myBART system. In response to this intrusion, BART has temporarily shut down the website, and have notified law enforcement authorities.

BART said Anonymous has obtained contact information consisting of names, email addresses, passwords, addresses and phone numbers from at least 2,400 of its 55,000 members, although it is still investigating the incident details. It is known that no financial information has been hacked as the myBART database doesn't store such data.

After hacking, Anonymous said in a statement, "BART has proved multiple times that they have no problem exploiting and abusing the people. First they displayed this by the two recent killings by BART police. We are Anonymous, we are your citizens, we are the people, we do not tolerate oppression from any government agency."