BART police officers push back a protester at the Civic Center station in San Francisco on Monday. (Jeff Chiu/AP)

After authorities for San Francisco’s Bay Area Rapid Transit, or BART, blocked wireless signals in certain stations on Thursday, angry demonstrators organized by a hacker group disrupted service at four busy stations during Monday’s evening commute.

Dozens of protesters wore the Guy Fawkes masks made popular by the movie “V for Vendetta” as they carried signs and banners accusing BART officials of censorship.

The hacker group Anonymous also hacked the agency’s Web site, posting images of Guy Fawkes and personal information of thousands of the passengers.

The cellphone blackout had been an attempt to head off protests over the July 3 shooting death of Charles Blair Hill by BART police. Police say Hill came at them with a knife.

While First Amendment scholars say they can’t remember a time when a public agency clamped down on private communication in this way, BART's chief spokesman, Linton Johnson, told reporters: “There is a constitutional right to safety... A lot of people are forgetting the fact that there are multiple constitutional rights.”

BART officials said they knew of no arrests or injuries.

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A man is pulled off a commuter train at the Civic Center BART station in San Francisco on July 11 after climbing on top of it during a protest against the July 3 shooting by transit police of Charles Blair Hill. (Eric Risberg/AP)