Twitter Circle is a feature that allows users to tweet to individuals included in private small groups only. This allows users to share secrets with selected people and the information is not revealed to the public.
But last month TechCrunch reported that tweets in the Twitter Circle could appear on the For You tab. There are even cases where Twitter Circle hacks are seen by unknown users.
TechCrunch has recently reported that Twitter has confirmed that Twitter Circle tweets have a bug that allows them to appear on the For You tab for the public to see. This tweet can be known to be specific to the Twitter Circle because the retweet button is turned off and there is a green label saying "Only people in the Twitter Group ... can see this Tweet".
However, sources say Twitter has already identified the problem and the issue has been fixed. So if you're confident with Twitter Circle you can now go back to sharing secrets or gossiping with individuals of your choice.