When I studied computer security concepts in University, I found that it was an exciting field to be in: images of late night hackers 'rattling doors' of our servers and we patching up security in an attempt to be one-up against any malicious attempts may have conjured up some adrenaline and romantic thrill. But thinking about it after the adrenaline had worn off, it was a terrible industry to be involved in, unless you have an addiction to adrenaline or heroism.
The fundamental fact of life is this: the bad guy only has to succeed once, and you on the security side, have to succeed all the other times. Nobody's going to say you've done a good job if you thwart a thousand attack attempts, but that one time that you left a vulnerability open, a thousand eyes cast blame on you.
Needless to say, I changed my mind about being in computer security. I guess I don't want to be a person who sees and speaks of different 'zones': restricted, secure, demilitarized, public; when it comes to real people and places. I don't want to live with paranoia thinking that someone's out to get us — all the time.
Once in awhile though, we hear of clever stories like this (and another retelling of the story from another angle here): of British military intelligence thwarting terrorist bomb-making factories in North Ireland. Another story linking it mentioned this story: to install a bug in a house with motion and noise sensors, they started shooting mints to the windows during thunderstorms, thereby triggering the alarm and the security people — who predictably associated thunderstorms with false alarms and began to shut off the alarm system during thunderstorm. Thus the spying party was able to drill the bug into the house wall during a thunderstorm when the alarm had been turned off. Mints were used because they quickly dissolve in the rain. Clever!
In military intelligence, the stakes are thousands of lives, civilian lives. I always thought of people working in it to be truly heroic, despite the countless times that we wish the whole transport security farce would just cease.