Reddit, the social media platform that has spawned some of the country’s most outrageous political conspiracy theories, has admitted its websites were penetrated during the 2016 U.S. presidential election by Russia.

According to an investigation by The Daily Beast, Russia’s notorious social media troll farm, the St. Petersburg-based Internet Research Agency (IRA), distorted political debate on Reddit.

Last month, the IRA was depicted as the centerpiece of special counsel Robert Mueller indictment of 13 Russians for interfering in the 2016 election.

The San Francisco-based Reddit, which helped give birth to the unfounded Clinton “Pizzagate” pedophile ring story and stoked suspicions over the death of DNC staffer Seth Rich, does not create any actual news or entertainment content. Instead it is purely a social news aggregator and discussion portal where members register to anonymously submit content.

Earlier this week, the firm’s co-founder Steve Huffman admitted the biggest problem was “indirect propaganda” which he argued was more complex to spot and stop.

The firm has removed “a few hundred” accounts suspected of spreading Russian propaganda, fake news and disinformation around the time of the election, Mr. Huffman wrote Monday in a blog post, adding, “of course, every account we find expands our search a little more.”

“As it’s an ongoing investigation, we have been relatively quiet on the topic publicly, which I know can be frustrating,” he continued. “While transparency is important, we also want to be careful to not tip our hand too much while we are investigating.”

This week, members of the Senate Intelligence Committee, who first voiced suspicion last year that Reddit could have been pray to Kremlin propaganda, announced they would soon question representatives from Reddit, in addition to the online sharing site, Tumblr, as part of their Russian election meddling probe.

There is growing concern that anonymous online forums, like Reddit, have become drivers of some of the internet’s most politically extreme and racially insensitive views — essentially providing breeding grounds for hate speech, fake news and foreign efforts to sow discord. They say that because such sites have almost no humans overseeing the unfiltered user-generated discussions, anything can take off.

Reddit for instance, in the lead up to the 2016 election, famously had trouble controlling the individual message board /r/The_Donald where members purportedly created discussions supporting Donald Trump.

In the wake of Mr. Trump’s election, the site also hosted a vigorous, but largely fictional, debate over the death of Democratic National Committee staffer Seth Rich, who Reddit users claimed had been murdered by Bill and Hillary Clinton for leaking party secrets.

This week Mr. Huffman addressed the overall issue of conspiracy on the website. “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,” he wrote. “I wish there was a solution as simple as banning all propaganda, but it’s not that easy. Between truth and fiction are a thousand shades of grey.”

More recently, the site has been heavily criticized for allowing the publication of fake videos of celebrities having sex, white supremacist content and conspiracy theories questioning the facts behind mass shootings.