A Facebook engineer took to Reddit late Monday to apologize for inadvertently blocking Imgur, one of the most popular image sharing sites on the Web, from the social network.

Users were prevented from posting any Imgur links to their profile pages and timelines on Monday, and were greeted by a Facebook error message telling them the links were being "blocked for being spammy or unsafe."

The false positive may have gone unnoticed by Facebook's estimated 950 million users late on Monday night, but the block was enough to provoke a backlash from users of Reddit, the hugely popular community site.

Imgur saw close to 30 billion pageviews over the last 30 days on more than 17.3 million uploaded images. Reddit, meanwhile, noted in a blog post in January that its own site had racked up more than 2 billion pageviews in the preceding December and had nearly 35 million unique visitors during the month.

Within a couple of hours after a picture of the Facebook error message was posted on Reddit, the image rocketed to the top spot on its homepage, attracting more than 800 comments.

Screenshot by Zack Whittaker/CNET; Source: Facebook

The Facebook engineer behind the block took to Reddit, apologizing on the thread for what happened. "This is actually my fault," he wrote.

Screenshot by Zack Whittaker/CNET; Source: Reddit

The problem occurred after the system Facebook uses to catch malicious and spammy links ran into a bug following a "bad URL that our automated defenses didn't catch," the engineer said, leaving Imgur blocked for a short, but unspecified, amount of time.

The engineer sought to fix the problem immediately, and followed his apology by uploading a picture of his "patriotic dog" to Imgur.

The engineer's post went some way to mitigating the faux pas in the eyes of Reddit readers: the apology comment is the most upvoted comment on the thread.

The Reddit comment's author shared the Twitter handle @fisherrider, which points to Matt Jones, a software engineer at Facebook working on the Site Integrity team. Jones subsequently tweeted a link to the Reddit comment: "Well, I guess that turned out OK after all."

A Facebook spokesperson told CNET in an emailed statement:

This morning, we mistakenly blocked an image hosting site as part of our spam prevention efforts and quickly worked to rectify the mistake as soon as we were notified. Facebook is a place where almost a billion people share click more than a trillion links a day. Our dedicated User Operations Team reviews millions of pieces of this content a day to help keep Facebook safe for all. Our policies are enforced by a team of reviewers in several offices across the globe. This team looks at hundreds of thousands of reports every week, and as you might expect, occasionally, we make a mistake and block a website we shouldn't have. We have already taken steps to prevent this from happening in the future and we sincerely apologize for any inconvenience.

Updated at 2:30 p.m. PT with a statement from Facebook.