A recent bug has been discovered by a small amount of users on the Skype support forums. The bug has been discovered to send small snippets of text conversations to other users. It appears to vary by user on how much of the private conversation is sent to other users but some have claimed that entire conversations have been sent. Skype have confirmed they are working on a fix and shall push out a notice for customers to update Skype. So it might be best to watch what you say on Skype until a fix is released.