Clifford Stoll at TED
Clifford Stoll was the guy, who found some hackers hired by the KGB in his system 20 years ago. In computer security he is known for his book “The Cuckoo’s Egg” (albeit it´s more a popular science book), which describes the hunt after the attackers. 2 years ago he held a presentation at TED. His style is a combination of Carl Sagan and Roger Rabbit (as a commentator at the TED site wrote) but it gives you many interesting insights. Really worth a look.