Yes UT2003 (and UT) servers are being attacked, if you have upgraded your server to 2225 (and 440) it will prevent your server taking part in the DDoS, however this will _not_ stop you from being attacked.
There is no way to stop from being attacked. If all the logging causes problems on your system you might want to surpress log entries. To Suppress log entires add a line "Suppress=xxx" to your ini file. Where "xxx" is the text you see in front of each log entry.
if you have "Suppress=NetComeGo" in your ini file it will no longer log it.
NetComeGo: Close TcpipConnection 127.0.0.1:3870 06/17/03 13:21:28
You might want to suppress the following entries during these attacks: