Facebook has started throwing a CAPTCHA prompt for all Google Blogger blog links. This means that when you want to share a blogspot.com link, or any link hosted by Google Blogger, Facebook won't immediately let you do so. Instead, you'll be prompted to verify that you are certainly a human and not a bot.

Try it yourself. Head over to Facebook and try posting a link (on your profile, on a group, on a Page) to any Google-hosted blog (here's a list), such as the Official Google blog or JQuery HowTo. You will get a CAPTCHA prompt like the one in the screenshot above. If you manage to prove you are a human, the link should go through. If you don't, it won't. Even more ridiculously, if you click cancel, Facebook will show you a post that looks like what you wanted to share, but the link will be just text, suggesting the post isn't there. If you refresh, you'll see that indeed it's not.

Facebook has likely started doing this automatically because thousands of spam links are hosted by Google Blogger. Unfortunately, this is now affecting legitimate websites. Meanwhile, thousands of spam links not hosted on Google Blogger are still getting through.

To make matters worse, the "What's this?" link in Facebook's "Security Check" window is broken. That means users who don't know what a CAPTCHA prompt is cannot easily find out. I'm told this is causing a lot of confusion for many Facebook users trying to share legitimate links.

One can argue this problem is not as bad as the issue three months ago, when Facebook completely blocked Snopes.com for being spammy or unsafe, since if you type in the CAPTCHA correctly, you can still post the link in question. On the other hand, this prompt doesn't affect just one website: Blogger provides hosting for hundreds of thousands of websites. To give you a better idea of Blogger's size, note that its Alexa rank is 43. CNET's is 88 and ZDNet's is 1,093.

Google bought the Blogger blog-publishing service in February 2003. Most of the blogs are hosted by Google at the blogspot.com subdomain. Up until May 2010, Blogger allowed users to publish blogs on other hosts, via FTP, and all such blogs that still exist are now hosted on Google's own servers, with their own custom URLs.

I was first alerted about this issue by the owner of The Bulldog Estate, which is hosted on Google Blogger but has its own custom URL. Ironically, his website helps Facebook users by informing them of spam and scams proliferating on the social network.

I expect that this is a mistake in the company's automatic spam-filtering system. I have contacted Facebook and will update you if I hear back.

Update on March 12 at 7:00 AM PST: The issue appears to be fixed. I have still not heard back from Facebook.

Update on on March 12 at 2:00 PM PST"To protect the millions of people who connect and share on Facebook every day, we have automated systems that work in the background to maintain a trusted environment and protect our users from bad actors who often use links to spread spam and malware," a Facebook spokesperson said in a statement. "These systems are so effective that most people who use Facebook will never encounter spam. In rare instances, these systems will require a CAPTCHA to be solved before users can post a link in an effort to stop spammy. We are constantly iterating on these systems and our always working to provide a better experience for those who use our service."

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