Had fun like this a while back.
Working for a small business that had a web hosting company set up, a malicious competitor came in to see the setup pretending to be a customer. He went home that nite and proceed to run any and every script or exploit short of DDOSing the boxes to get them down but there was an firewall up that logged his IP, recorded all of the attempts to exploit; and eventually banned his IP automatically.
He called in first thing next morning, all excited claiming that our servers were down... Was dead silent and then hung up when I explained to him that his IP address was banned due to the exploits he threw at the server the previous night. Never saw or heard from him again.