Some of the biggest pro-Bernie Sanders groups on Facebook were briefly taken down Monday evening in a targeted attack by Hillary Clinton supporters.

The groups Bernie Sanders Activists, Bernie Believers, BERNIE OR BUST, Bernie Sanders Revolutionaries, Bay Area for Bernie, Bernie Sanders 2016 — Ideas Welcome, Bernie Sanders is my HERO, and Bernie Sanders for President 2016 were all taken down in the attack. The pages in question were reported to be down for about three hours, from 9 p.m. to midnight Monday night.

Collectively, these groups are home to more than a quarter million Bernie Sanders supporters, and some have been in existence for nearly a year, having been launched shortly after the Vermont senator declared his intent to run for president in 2015.

The groups were targeted by online trolls, who posted pornographic images and reported the groups to Facebook admins. Some legitimate Bernie supporters even reported seeing images containing pedophilia, according to reporting from Heavy.com.