A banned link to a blog post about a cancer sufferer's protest against UK privatisation of the NHS was "mistakenly" marked suspicious, Facebook said in response to allegations of censorship.
Bristol blogger Kerry-Anne Mendoza was "confused and saddened" when links to her Scriptonite Daily blog were suddenly marked as spam by Facebook and removed from the social networking site after the post - charting Mark McGowan's journey to present a petition to 10 Downing Street - received more than 1,000 shares.
A second blogger, Tom Pride, alleged similar treatment after his blog was declared suspicious by Facebook following a satirical article about the Department of Work and Pensions and ATOS, leading to accusations that Facbeook's anti-spam procedures left it open to attempts at political censorship.
Pride claimed in a post on his blog that a JobCentre Plus worker "openly bragged" to him that she had made a complaint to Facebook before traces of his piece were removed.
A Facebook spokesperson said: "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.
"These systems are so effective that most people who use Facebook will never encounter spam. They're not perfect, though, and in rare instances they make mistakes.
"This link was mistakenly marked as suspicious and we have already started to make adjustments to our classifier. We look forward to learning from rare cases such as these to make sure we don't repeat the same mistake in the future."
Facebook declined to comment on why the material fell into its spam filters.
The comments came as Channel 4 News revealed Facebook had refused to take action after weeks of complaints about a YouTube video being shared on the site showing a baby being beaten, only removing the content after the broadcaster intervened.
#c4news tonight - how Facebook said a video of a woman beating up a baby was not a breach of its rules
— alex thomson (@alextomo) April 26, 2013
#c4news week after week Facebook allowed baby-beating video - til we intervened last night
— alex thomson (@alextomo) April 26, 2013