For UT2004, you can ban by player GUID (a hash of the CD key) or IP. With the game abandoned by Epic, a number of key generators have cropped up, which makes GUID bans useless. IP bans only go so far with VPNs costing $2 these days.
The main solutions we have today are IP ban + VPN blocking using a database of known VPN subnets and adding them all to the firewall, and a similar fingerprinting technique which scans their folder structure of certain system folders.
The main solutions we have today are IP ban + VPN blocking using a database of known VPN subnets and adding them all to the firewall, and a similar fingerprinting technique which scans their folder structure of certain system folders.