The GCAT backdoor is a fully featured backdoor which could be controlled by using Gmail as a Command & Control server. This means that the attacker can send instruction to remote system through a Gmail account. The code related to the backdoor is available on GitHub, the repository included the following two files: Gcat.py a script thats used to enumerate and send commands to the bots.py is the backdoor.py. The traffic from the Gmail account will never raise suspicions in the administrators of a network and will never trigger any alarm, also consider that the command and control architecture will be always up and reachable.”]
Source: http://securityaffairs.co/wordpress/40537/hacking/gcat-backdoor-gmail.html