The propensity for people to post porn evidently prompted Twitter on Wednesday to stamp an adult rating on an updated version of its Vine video-snippet sharing software.
Concerns were raised about two weeks ago, after adult content was bared briefly in an "Editor's Picks" section at Vine.
Twitter apologized for the mistake, blaming "human error" but providing little detail, and quickly removed the video.
Vine, a service that lets people share video snippets from iPhones or iPod touch devices, was launched in January by the globally popular one-to-many message sharing service.
Perpetually looping video clips, up to six seconds each, can be shared using Vine or easily embedded in "tweets" fired off at Twitter.
A new version of the free Vine application, available at Apple's App Store on Wednesday, required people to confirm they are at least 17 years old before they can download the software.
The adults-only rating cited "frequent/intense sexual content or nudity" along with "mild" realistic violence, crude humor, profanity and drug use.
Twitter did not respond to a request for comment.
Twitter bought Vine, a startup based in New York, in October, prompting talk the messaging service intended to do for smartphone video what Instagram did for pictures.
Twitter in December added Instagram-style smartphone photo sharing features after the Facebook-owned service made it impossible for Internet users to integrate its images into tweets.
Previously, Instagram pictures shared in messages tweeted from smartphones could be viewed unaltered at Twitter.