I think this is the most important question regarding online games on Linux, and aren't most games online these days?

I think that the solution is radical: I think that as much much time and effort should be put into making the binary unhackable as is put into the game. Ultimately, DRM(1) is a game, and a lot of programmers are addicted to breaking it anyway.

What's funny about DRM in the case of an online game is that it's actually a feature that customers would pay extra for, and a premium for quality DRM. Hopefully, we'll have good companies and groups creating it, and online games (whether given away or sold) will advertise and brag about what kind of DRM that they're using.

(1) I'm using the term DRM because I can't figure out a better term - but it's more like tamper management, isn't it?