This is indeed an exploit, bug, whatever you want to call it. You are abusing the mission system by hopping instancing over and over until you have almost 100 million in missions. It should be patched, I know numerous people now who have literally made 500m credits in the past few days and even hit trade Elite in those few days. To put this into perspective, trade elite takes a normal user with 8-10m/h trade routes, approx 1 month with 3-5 hours a day of work. Is that fair to anyone who actually put in the effort for Elite? No it is not. It's an insult to anyone who worked hard for their stuff. It's also worse than the dumbing down of the game that Power Play did with it's 50m per week non sense. & even without hopping instances, these pay far too much, you can make 9m from one mission, and sometimes there are 2 to 5 on the mission board without an instance hop anyways. That's already over a day or 2 of work in half an hour worth of missions right there.
FIX THIS FRONTIER, IT ISN'T RIGHT.