SAN FRANCISCO - Four San Francisco subway stations shut down temporarily on Monday during a demonstration organized by the hacker group Anonymous over police brutality and free speech.

The Bay Area Rapid Transit commuter train service had shut down cell phone networks in some stations on Thursday to stop demonstrators organizing a protest over the fatal shooting of a man by police last month.

"This was a complete silencing of the people." said Carlos Wilson, a 41-year-old gay rights activist who came to protest police brutality and the shut-down of the mobile phone network last week.

A few dozen protesters turned out for Monday's rush hour action, which ended when authorities shut down the Civic Center station. Later, three other stations closed briefly, apparently due to crowding.

Police said there were no arrests, although officers arrived dressed in riot gear.

Cell phone service was left on in the station during the action, and some protesters took that as a sign of victory.

"I have more cell service now than usual on BART. I think what they did last time was an empty threat. I have full bars," said Beck Simmons, a 21-year-old student.

Anonymous, a loosely knit group that has attacked financial and government websites, had called for protesters to descend on the station at 5 pm and media widely publicized the plan.

Would-be protesters were encouraged to download software for short-range mobile-to-mobile messaging, in case the in-station networks are shut down again.

BART said a website for its users, myBART.org, had been hacked over the weekend, and contact information from at least 2,400 people had been stolen.