I wonder if it would be possible to build security into a future firmware update, and somehow make that firmware compulsory for entering times on wipeout-game.com and for playing online.

Even if it is possible to cheat, I don`t think it`s necessarily a disaster. Cheats aren`t difficult to spot, and it just means a bit of human intervention would be required to keep the tables clean and weed them out. You could cheat your way from 500th to 50th, but who would care and who would bother? You could cheat yourself into massive leads but no-one would believe you.To cheat convincingly, beating the best honest pilots by just the right amount to appear believable could be such a difficult task that it might be more effort than the average cheat would be prepared to take on. The honest players, who are by far the majority, could just crack on with the racing.