You might want to change your login and password if you've ever used the myBART.org site for San Francisco's Bay Area Rapid Transit service.

Members of the online hacktivist group Anonymous have started up their 48-hour attack on San Francisco's Bay Area Rapid Transit (BART) subway service, launching their first salvo against the mybart.org website in the form of a few cyber-defacements and a massive data dump of users' emails, phone numbers, addresses, and login credentials.

Promises to take the official BART website offline starting at noon PST have yet to come to fruition, however: The site, bart.gov, remains online and fully active as of this article's writing. But that hasn't stopped Anonymous members from hitting other targets. The California Office of Traffic Safety's "California Avoid" site has been defaced as well.

An official Anonymous press release outlines the group's primary battle plans for the next two days, which includes a "massive Black Fax and E-Mail Bomb" against BART. The move is apparently designed to stifle the organization's ability to communicate, a direct response to of its cellular capabilities in an attempt to thwart planned protests. Anonymous has also planned a peaceful protest of its own for Monday, scheduled for 5 pm (PST) at BART's Civic Center station in San Francisco.

"#OpBART is an operation geared toward balance - toward learning. You do not censor people because they wish to speak out against the wrongs the wrongful things occurring around them," reads the group's press release. "The Bay Area Rapid Transit has made the conscious decision of ordering various cell phone companies to terminate services for the downtown area inhibiting those in the area from using cell phones - even in the case of an emergency."

BART officials have acknowledged that they are aware of Anonymous' plans to take down the organization's website and launch a protest, and officials have already issued updates to alert site users and riders about the planned disruptions. And the alleged "Black Fax" campaign by Anonymous hadn't actually done anything as of this morning, when BART officials were interviewed by CNET's Eric Mack.

According to the official Anonymous Twitter feed, the group's release of thousands of user names and passwords for the mybart.org website is just the first start in its cyber-campaign.

"We're not done yet folks... we're just getting warmed up," reads a message posted to @youranonnews.

For more from David, follow him on Twitter @TheDavidMurphy.