What's the best way to monitor a system for attacks?
A thread on firewalls in the Coffee Lounge section made me realize that I have no idea how to monitor if my online computer is being probed or attacked or whatever. I tried googling, assuming there were programs out there that did this, but I couldn't come up with much (possibly because I'm not sure the right terminology to use to look for an answer). Anyway, are there system logs that record all of this in a way I could figure out or do I need a program to monitor the system for attacks?
Thanks for your help.