Trustwave’s SpiderLabs analysts discovered a hidden backdoor in Skype for Apple’s Mac OS X operating systems. The backdoor resides in the desktop Application Programming Interface (API) that allows third-party plugins and apps to communicate with Microsoft-owned Skype. The researchers have provided proof-of-concept Objective-C code that initiates the connection process without asking the user for permission for the process to attach to Skype. Trustwave notified Microsoft of the vulnerability in October, and the company has patched the issue in Skype 7.37 and later versions.
Source: https://thehackernews.com/2016/12/hacking-skype.html