WAAAAAAAAAAAY back in the day, a misconfigured, or brute-forced PBX could present a dialtone to an inbound caller, allowing calls to originate from the system.

WAAAAAAAAAAAY back in the day, a misconfigured, or brute-forced PBX could present a dialtone to an inbound caller, allowing calls to originate from the system. (Actually, this is probably easier with VOIP trunk credentials nowadays) Once discovered, this would quickly pivot and feed a redialer service and run up your phone bill something fierce. Till the next billing cycle, the system owner might be none the wiser! If there is money to be made selling something obtained for free, legally or illegally, it will be abused.