Reddit says it has identified and removed hundreds of Russian propaganda accounts, a few days after reports revealed that Russian trolls were active on the platform during the 2016 U.S. presidential election.

In a post Monday, Reddit co-founder Steve Huffman said his site operators had been investigating for awhile and had found a few hundred accounts suspected to be of Russian origin or linked to known sources of Russian propaganda.

“Of course, every account we find expands our search a little more,” he said, also claiming the “vast majority” of the suspicious accounts were banned back in 2015–2016.

An even bigger challenge was the problem of “indirect propaganda,” where content produced by accounts now known to be Russian trolls was enthusiastically shared by Trump supporters on subreddits such as r/The_Donald.

He cited the case of the 136,000-follower Twitter account @TEN_GOP, which appeared to be run by Republicans in Tennessee but is now known to have been a Russian troll account.

“@TEN_GOP’s Tweets were amplified by thousands of Reddit users, and sadly, from everything we can tell, these users are mostly American, and appear to be unwittingly promoting Russian propaganda,” he wrote.

“I believe the biggest risk we face as Americans is our own ability to discern reality from nonsense, and this is a burden we all bear.”

Reddit’s investigation followed a report from The Daily Beast, based on leaked internal data from Kremlin-backed troll farm the Internet Research Agency, that confirmed Russian trolls were active on the site, as well as Tumblr, in their mission to spread disinformation, divide Americans and disrupt U.S. politics.

Special counsel Robert Mueller has charged 13 Russians, all connected to the Internet Research Agency, in his ongoing probe.

Congressional investigators looking into the Russian issue intend to question Reddit and Tumblr over their involvement, the Washington Post reported Monday.