My favorite security show each year is one at which there are no sales pitches, the speakers favor black T-shirts and dyed hair over suits and ties, and the talks tend to be controversial enough to prompt legal threats and even arrests.

I'm talking about Defcon, which starts Thursday and runs through Sunday. The event turns part of the Las Vegas strip into a geek equivalent of "Animal House" for a three-day weekend every summer.

Started in 1993 by Jeff Moss, aka Dark Tangent, Defcon bring...