Private files belonging to America’s biggest police union, including the names and addresses of officers, forum posts critical of Barack Obama, and controversial contracts made with city authorities, were posted online on Thursday after a hacker breached its website.

The Fraternal Order of Police (FOP), which says it represents about 330,000 law enforcement officers across the US, said the FBI was investigating after 2.5GB of data taken from its servers was dumped online and swiftly shared on social media. The union’s national site, fop.net, remained offline on Thursday evening.

“We have contacted the office of the assistant attorney general in charge of cyber crime, and officials from FBI field offices have already made contact with our staff,” Chuck Canterbury, the FOP’s national president, said in an interview. 

The FBI did not respond to a request to confirm that it was investigating.