Twitter issued a fix on Sunday for a bug that affected 93,788 protected Twitter accounts. The issue was that protected accounts could be followed by people who added them via SMS rather than via the app or website. Twitter has removed all of these unapproved follows, and taken steps to protect against this kind of bug in the future. The scope of this bug was small in terms of affected users, but that does not change the fact that this should not have happened. The bug has been fixed since November 2013.”]
Source: https://www.csoonline.com/article/2136250/twitter-fixes-protected-tweet-bug.html