The pair used a trick "known to terrorists and teenagers alike."

As more details emerge about the event that can fairly be called L'Affaire Petraeus, we're learning more about how the former CIA director and his biographer conducted their relationship.

One of those ways? Craftily.

To conduct their communications over email, the Associated Press reports, Petraeus and Paula Broadwell established a joint email account. They then composed emails to each other without sending them -- saving the messages, instead, as drafts. That allowed them to access messages and reply to them ... to communicate via email without actually sending emails. Which meant that their messages would be relatively hard for outsiders to trace. 

This is a pretty basic method of sub-rosa communication, to be sure. It is also rather brilliant. Which is perhaps why it is a favorite not only of teenagers trying to escape the gaze of meddling parents, but also of a group that is even more skilled at operating undetected: terrorists. Here, according to Frontline, is one of the "tricks" that members of al Qaeda and similar networks use to communicate covertly across the world:

One terrorist drafts a Web-based e-mail and instead of sending it, saves it to the draft folder, accessible online from anywhere in the world. The other terrorist can open the same account, read the message, and delete it.

Sounds familiar. Petraeus and Broadwell, both counterterrorism experts, put their knowledge to use: They put al Qaeda's system into a new, but similarly sensitive, context. The ironies in that terrorism/infidelity connection are many, but one of them is this: The very thing that seems to have bonded the pair in the first place -- their shared insight into the workings of a world that is so foreign to most civilians -- is also what helped them to conduct their relationship. As members of the military, the two traded in secrets. It just happened that to be that some of the secrets they traded were sent, and received, in private.