The warriors of the future: software developers, one with spiked hair, another who looks too young to vote. They are working on the largest software program in Defense Department history, a project that the military says dwarfs Microsoft's Windows. The project is the heart of Future Combat Systems, the Army's most expensive weapons program.

"There's nothing like it, ever," said Loren B. Thompson, a defense consultant at the Lexington Institute, a public policy think tank. "Nobody has ever before attempted to integrate a software system as remotely complicated as FCS is going to be. It is many times more complicated than any other defense program."

"Magic under the hood" is what Boeing engineer Paul D. Schoen, one of the project leaders, calls the software. Others in the military call it Windows on steroids. John Williams, a chisel-jawed sergeant stationed at the Boeing plant who has served in both wars with Iraq, isn't interested in what it's called.

Military experts question the ability of the code to withstand an onslaught of attacks -- from hackers, worms and Trojan horses -- that could leave soldiers vulnerable.