This what killing games the abuse of any source.
As per account limits, games should be designed in a way where MAC Addresses should be integrated with its engineering to verify authenticity. This method would require hard programming where user should not alter the games config files. MAC address authentication should work in this form:
User launches the game--> Game config file requests to central server that the MAC address of the PC is registered in the database--> Central server sends an acknowledgement confirming that the game configuration has not been altered and MAC address is registered ---> user gets prompted for username and password to launch the game.
The following technologies use the MAC in a form of a identifier:
802.11 wireless networks
IEEE 802.5 token ring
most other IEEE 802 networks
So why not design the game in this form?