If you have AMX MODX installed then Never install WebMod Plugin as it is very easily exploitable and an attacker can gain access to your PC files , avoid it at any cost because its patch will not be released in near future.
Disable ICMP request by registry editing (be VERY CAUTIOUS while you edit registry).
Proceed
Go to Start --->Run --->Type "regedit" --->Hit enter/return on keyboard ---> open(in order)
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
Method to take Registry Backup of ICMP value
Click "File" (top left of registry window) ---> Select "Export" ---> in Export Registry Window , slect to save it on Desktop ---> give any name to file , i choose "ICMP_ENABLED" for "File name:" option ---> Click Save button --->See if new file appears on Desktop (Donot close Registry window at this point).
Now we may safely proceed to Disable ICMP Requests
Method to Disable ICMP Request:
with this path opened in registry
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
highlight "Parameters" by single click on it --->now look at the right side of window --->Find "EnableICMPRedirect" option , its a DWORD value, change its value from 1 to 0 (zero).
---->Close the Registry window ----> Reboot your Computer for the changes to take effect.
Hope this should solve your CounteStrike 1.6 DOS attack problems to certain extent but the truth is that the DOS or DDOS attacks are considered to be the most dangerous attacks which are capable enough to bring any system down.... but definately thier effects can be minimized to very low level.
Thanks !