For several hours today, Facebook blocked links to “bsdetector.tech,” the website for a popular browser extension that detects and tags disreputable news sources.

“This message contains content that has been blocked by our security systems,” an error message told users when they attempted to link to the site on Facebook. “If you think you're seeing this by mistake, please let us know.”

Daniel Sieradski, the creator of B.S. Detector, took to Twitter this morning to point out the problem:



.@Facebook is now blocking links to the B.S. Detector!!! pic.twitter.com/gUagoe3AH2 — daniel sieradski (@selfagency) December 2, 2016

here's proof that 4 hours ago you could link to the plugin's homepage https://t.co/gmXWlmIIKg pic.twitter.com/iGnPjm246Q — daniel sieradski (@selfagency) December 2, 2016

It’s unclear why Facebook blocked the extension’s page, but it began working again this afternoon.

Created to correct for fake news floating around the web, B.S. Detector works by using a list of domains with known issues, and then flagging links to those sites. Categories like “fake news,” “state news,” and “conspiracy theory” appear next to the relevant links and pages.

The tool gained some accidental notoriety late last night, when TechCrunch erroneously reported the tool was a feature built by Facebook itself to detect fake news. TechCrunch later updated the story to note it was seeing B.S. Detector.

Facebook did not return a request asking for clarification on why the site was blocked.

Update, 2:58PM ET : Facebook is again allowing links to the site.

Update, 12/3, 4:42PM ET: Facebook provided the following statement: