The Secret Service is investigating reports that members of the activist hacking collective Anonymous have posted Republican presidential front-runner Donald Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE’s personal information online, including his Social Security number.

“The U.S. Secret Service is aware of the Internet postings of Candidate Donald Trump’s personal information,” a Secret Service spokesman told TIME. “We are working with the Federal Bureau of Investigation in this matter.”

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In addition to his Social Security number, the information allegedly includes Trump’s mobile phone number, the name and contact information for his lawyer and the names of some of his family members.

A Twitter account that regularly tweets on behalf of the group has already denounced the information as “outdated,” calling the account that released the data “not a credible source.”

Anonymous recently announced a “cyber war” against Trump, urging its followers to launch a barrage of cyberattacks on April 1 to expose the “appalling” GOP presidential candidate.

“We need you to shut down his websites, research and expose what he doesn’t want the public to know,” a person wearing the group’s trademark Guy Fawkes mask says in a video posted to an Anonymous YouTube channel. “We need you to dismantle his campaign and sabotage his brand.”