A tweet was published Wednesday morning that contained a link to the names and addresses of more than 100 BART police officers. The international group of hackers called 'Anonymous' assumed responsibility.
Email addresses and passwords were also leaked on Wednesday.
"I can't believe that this type of criminal act happened," BART police officer representative Jesse Sekhon said.
Sekhon's information was among the names and addresses leaked. BART's Police Chief Benson Fairow said the FBI is investigating the matter.
There is concern for the safety of the officers now that their personal information is out in the open.
"It's just as wrong, and even more so in some cases than the average citizen," Fairow said.
"We're in the process of advising our members to contact their local jurisdiction to ask for extra patrols around the neighborhoods when they are not at home," said Sekhon.
This is the second Anonymous cyber attack in less than a week. On Sunday, the group managed to access the back end of a BART customer service website. After harvesting customer information, the group posted personal information for around 2,500 BART patrons.
The group has claimed responsibility for the attacks after BART decided to shut off cell service last Thursday when they feared protests were planned at the Civic Center Station.
"The public is going about their business. They are not a part of this," said BART Board President Bob Franklin. "Bring it to the BART board. We are going to be meeting next week. Let's talk about it there -- leave the innocent people out of this."