David Petraeus might not have been a good enough spy to avoid getting busted in the arms of his push-up-crazed biographer, but he did use a damn clever trick for sneaky correspondence: the neglected draft folder.
So simple. So obvious, even. Maybe you've used it yourself—though it certainly didn't occur to me in yesterday's roundup of 21st century cheating techniques. The AP reports the spy master didn't even send emails to Broadwell—they just let them sit: