While the flaw has been patched up, Ramshath said in a Medium post that it has "significant privacy implications" and could spark "trust issues" among users who rely on the feature to share private media.
The security flaw, which only impacted iPhone users, allowed anyone to see 'View Once' content in the stored media section of their app Settings.
The creators behind the messaging app finally caved after billions of users demanded the change.
Chat themes can be set as the same for all contacts, or users can set individual layouts.
A separate but similar 'View Once' loophole emerged last year, when hackers were able to save and share copies of private media.
