Hello everyone
I am make iptables rules for CoD2 and it works:

sudo iptables -A INPUT -p udp -m string --algo bm --string "INVALID_CDKEY" --sport 20700 --dport 28960 -j DROP
sudo iptables -A INPUT -p udp -m string --algo bm --string "BANNED_CDKEY" --sport 20700 --dport 28960 -j DROP

...but it doesen't work for CoD UO Why?? Whats differents? CoD2 and CoD UO have a working master servers. Help pls!