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Anonymous, the loose collective of online hackers, issued an ominous warning to President-elect Donald Trump ahead of his inauguration, telling the billionaire he's going to "regret" the next four years.

A supporters of the activist group Anonymous wears a mask during a protest in London, Britain. Stefan Wermuth / Reuters

On Twitter, the group put out a call to action to its followers, urging them to expose any potential compromising information they can find about the soon-to-be new leader of the free world.

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The group tweeted at Trump, repeating unsubstantiated allegations that he has "financial and personal ties with Russian mobsters, child traffickers, and money launderers."

"This isn't the 80's any longer, information doesn't vanish, it is all out there. You are going to regret the next 4 years. @realDonaldTrump," reads a tweet from @YourAnonCentral, an account used to disseminate information amongt the hacker group.

Trump, a usually trigger-happy tweeter, seems to be ignoring the threats for now.

Trump has long been in Anonymous' crosshairs, with the group declaring war on him last year when he was a candidate for President of the United States.

Related: Trump Information ‘Leaked’ by Anonymous Has Been Online for a While

In March, private information about Trump was "leaked" by hackers claiming to be a part of Anonymous, including a cell phone and social security number. However, it was later proven that information wasn't new and had been floating around online for some time.