[litheon]

Command and Control Server (C2) refers to the infrastructure required to command and control malware of various forms.

The author basically found a creative use of Hinge’s infrastructure and proved it could be used to control malware.

[lisbbb]

But the malware was encoded as an image, how is it runnable on the target's smartphone?

[richbell]

The purpose of command and control servers is to send and receive data to victims devices.

A secondary goal is to do so while evading detection. This is why many threat actors piggy-back off of legitimate services, it disguises the malware communications and avoids directly exposing the upstream C2 instance.