Multiple Facebook pages supporting Democratic presidential candidate Bernie SandersBernard (Bernie) SandersDemocrats' CNN town halls exposed an extreme agenda Buttigieg says he doubts Sanders can win general election Meghan McCain: Bernie Sanders supporting prisoners being able to vote 'bats**t insane' MORE were abruptly removed from the social media network late last night following a cyberattack.

The pro-Sanders pages — which include Bernie or Bust, Bernie Believers and Bernie Sanders is my HERO — were collectively followed by over a quarter-million supporters of the Vermont senator, and many had been operating continuously since Sanders launched his campaign last year.

The attack began around 9 p.m. EDT and lasted until just after midnight, when most of the pages recovered their accounts.

According to eyewitness reports, the pages were flooded with pornographic images in what appeared to be coordinated fashion and then flagged for obscene content, prompting Facebook to remove them.

"We had what looked like a kiddie porn posted in one of our groups today,” said Sanders supporter Erica Libenow, according to Heavy.com. "I reported that one. Seriously made me want to vomit.”

A Facebook spokesman confirmed to The Hill that a number of pro-Sanders groups as well as other pages "were inaccessible for a brief period" due to the company's automated policies being "applied incorrectly."

"We corrected the problem within hours and are working to improve our tools," the spokesman said.

At least one Facebook user linked to the pro-Hillary ClintonHillary Diane Rodham ClintonDavis: The shocking fact that Mueller never would have accused Trump of a crime Trump says he would challenge impeachment in Supreme Court The Hill's Morning Report - Will Joe Biden's unifying strategy work? MORE group Bros 4 Hillary was reported to have participated in the attacks.

The Bros 4 Hillary team disavowed the user in a statement posted Tuesday morning, which condemned any "harmful or offensive rhetoric or harassing behavior targeting supporters of any other candidate in the race.”

Several websites and online forums and website attempted to draw a connection between the attacks and Clinton ally David Brock’s social media initiative, Barrier Breakers 2016, after noting that the former Bros 4 Hillary member had recently “liked” the initiative on Facebook.

In a statement to The Hill, Correct the Record denied any involvement in the attacks.

"Correct the Record's Barrier Breakers 2016 had nothing to do with this," said Elizabeth Shappell, the group's communications director. "Currently, Barrier Breakers is exclusively engaged in positive messaging supporting Hillary Clinton."

This story was updated 2:26 p.m.