Here is a snippet of a response from Wilders:
BlackFog sits at layer 3 of the Network stack and watches all outbound traffic and watches for anomalies in behavior, this includes data leaking to known C&C servers, crypto mining sites etc. We look at how protocols are formed, what it is sending, how and where to determine if it is legitimate and block accordingly. We have about 12 different parameters (many more under development) that are used to determine legitimacy of the traffic. In addition we monitor executable location to prevent files being dropped on your machine. As pointed out this is very complex to do and it is done in real time.
We designed this to be no intrusive and minimize false positives.
We have a lot of blog articles that talk about each aspect in a lot more detail if you are interested. I would point you to the following as a starting point:
All About Data Exfiltration