Hack it just like any other node. ECM and ECCM has to do with jamming a signal. If you wanted to deny the drone you could jam it's signal, or jam the rigger in the same regard.

Alternately, you can intercept the wireless signal between the hacker and his drone, and spoof your own commands to the drone instead. Either way you do it though, the rules are less than clear, so many people have posted house rules and campaign interpertations of how the process is supposed to work.

Bull was soliciting questions for a FAQ that he was going to be developing with input from as many of the original authors as he could get in touch with, and a large percentage of the questions dealt with exactly this topic, so hopefully, sometime in the near future, there may be some answers out there as to how the rules for hacking drones were intended to be used.

You can do this with other Matrix systems too (Host->Camera for example) and it all functions the same. All any of us have are the core rules, so if you are looking for more than what's in RAW, you are in the same boat as the rest of us.