For some onlookers, David Petraeus’ affair with his biographer Paula Broadwell offered a lesson in hubris, foolhardiness and the true meaning of the word crush. Others simply learned a new way to leave stealth messages for their squeeze on the side: Petraeus and Broadwell communicated via a shared Gmail account. One would write a mash note and leave it in the draft folder without sending it. The other would then log on and check what surprises awaited in the draft. The technique, which is said to be employed by terrorists as well, leaves no e-mail signature. But as the ex-lovers and the entire rest of the planet found out, it’s not spook-proof.