the technology for intrusions is far ahead of the technology for defenses, and we need to catch up. >> reporter: how often are there attacks on the pentagon's networks? >> there are attempted intrusions thousands of times a day. >> reporter: these intrusions are not pranks but espionage conducted by foreign intelligence agencies. cyber spies could be lurking undetected inside one or more of the defense department's 15,000 computer networks. they're in and we don't know it? >> it's entirely possible. three years ago, we found that someone had gotten into our classified network, and we didn't think that was possible because it's completely separate from the internet. >> reporter: a foreign intelligence agency-- lynn won't say which one-- penetrated a classified computer network used by the u.s. central command, which runs the wars in iraq and afghanistan. how long were they in? >> it was probably a matter of months.