Assuming your ISP deals out dynamic ips

If they do, you're in the clear.
Mine does, so I'm pretty much pwnage.

you have to pay more for a static ip usually, so they probably do.

*sigh* You cannot ban by mac address on the internet. Layer 2 information gets stripped as soon as it gets to an IP router. And no, assigning a dynamic IP address does not give you a new MAC address.

For those interested, if you look at the MAC address of the frame coming from someone on the internet, it might look exactly like your gateway's MAC address, which you might not want to ban.

We can, and have, banned entire IP ranges; takes care of the dynamic IP right quick. (Granted, I think we banned the entire state of Florida trying that once - takes some finesse with da whois sometimes.)

Really though, if someone has a Steam ID generator, and some internet smartz, there's not a whole lot we can do, save ban him one IP range at a time until it's no longer worth his while. We've rarely come across anyone that persistent, but last I recall it happening (Ferdog), we managed to beat them down eventually.

It would get all the hackers and exploiters :p

If they get a new SteamID and a new IP range and come in under a pseudonym and come back and start acting like an ass: they get banned again.

If they get a new SteamID and a new IP range and come in under a pseudonym and come back and DON'T act like an ass: nobody's the wiser, and nobody cares.