I have an NT4.0 Network. I have PDC BDC proxyserver exchange server etc. Other then those I have a member server which stores some important files and stuff. I need to have a best intrusion detection program that would easily run on NT4.o member server. For security reasons I have un-shared all my drives and I've hidden my computername from the network.
But I still need to know if some one tries to enter or actually entered into my system and messed with my stuff.

Is there any good intrusion detection software..(free) that would secure my member server?