Observe them as they cavort around in the server. Log their conversations with each other. Study them like you'd watch insects under a magnifying glass.
That's the basic concept behind honeypots and honeynets, systems that are set up specifically so that security experts can secretly observe crackers in their natural habitats."
Michelle Delio, "Honeypots: Bait for the Cracker," Wired News, March 7, 2001
distributed denial of service
man in the middle attack
white hat hacker