Tumblr is working to resolve an issue causing seemingly random content to be posted to people's blogs that they didn't put there themselves, with pornography showing up in some instances.
The issue has affected only a small number of blogs, according to a message posted to Tumblr's Twitter account. The company's engineering team is working quickly to repair the issue, Tumblr said.
The social network could not be immediately reached to comment further.
Affected users have been posting comments to the site detailing their problems with the issue, using either the Tumblr Support or Tumblr Help tags.
Some of the content that was randomly posted was innocuous, but in other cases it was more graphic.
"Help, blogs that I'm not following are all over my [dashboard] and they are full of porn," one user said on the site.
Tumblr is no stranger to porn or other adult-oriented content, which it does allow on the site. Users who regularly posted sexual or adult-oriented content to their blogs are encouraged to flag their blog as "not suitable for work," which lets other users who do not want to see NSFW content avoid it.
Tumblr on Tuesday night also experienced some site issues preventing some people from updating or adding content to their blogs on their own, but it is not clear whether those problems were tied to the issue causing the random posts.
Yahoo announced its acquisition of the social network for more than US$1 billion in May. The deal was partly aimed at boosting Yahoo's revenue by giving it a larger slice of the social media advertising pie.
Advertisers started putting sponsored posts in users' feeds on the desktop in late May. It is not clear whether advertisers were also affected by recent posting issues.