I don't dispute that banks create money and greatly affect the money supply. Under normal conditions, the banks stay pretty close to their reserve requirement,

I don't dispute that banks create money and greatly affect the money supply. Under normal conditions, the banks stay pretty close to their reserve requirement, so a hacker suddenly creating a gigantic new loan at a bank is likely to push them over the limit and draw attention, either immediately or when somebody tries to move the money to another institution. But at present, many banks do have big excess reserves, so getting away with it is more plausible. It essentially becomes a loan the bank didn't really intend to make.