In an effort to cover a trail of messages between him and his mistress, former CIA Director Gen. David Petraeus reportedly used a tactic favored by terrorists and teenagers -- communicating via draft e-mail.

Petraeus and Paula Broadwell, the co-author of Petraeus' biography and the woman he was having an affair with, set up private Gmail accounts in order to communicate, the Associated Press reported today. In addition to creating the e-mails under false identities, Petraeus and Broadwell decided to exchange some messages using the draft function, as an added precaution.

Instead of actually e-mailing each other, they would compose and draft messages but not send them. The other person would then log into the same account and read the drafts. This made those messages harder to trace, and the tactic has been used in the past by terrorists and teenagers, an unnamed law enforcement official told the AP.

Apparently, this trick has been around a while. PBS Frontline mentioned it in a 2005 special on terrorist tricks and counter-measures.

The e-mails, discovered after an investigation into "harassing" e-mails allegedly sent from Broadwell's e-mail account to another woman, was what ultimately led to the general's resignation. The investigators initially thought the case "wasn't worth pursing" since the e-mails didn't seem too menacing, according to the Daily Beast. Petraeus was barely mentioned in the electronic messages, a source told the news site.

It must have been an unimaginable turn of events for the general who is known to be a prolific e-mail user, as well as a careful one, according to The Washington Post. While most of his counterparts weren't as quick to adapt to e-mail as a form of communication, the Washington, D.C., press knew Petraeus' affinity for technology. He was constantly checking his e-mail and was known to have two terminals open in his armored vehicle: one for classified information and one for an open Internet connection. Petraeus even bragged that he was the first CIA director to install an open Internet connection in his office, according to a reporter.

Just having an e-mail outside of his work e-mail set him a part from other high-ranking officials. Reporters said he e-mailed with the media frequently, but he was always very careful about the message he sent. It sounds like he was just as careful with personal e-mails, but it wasn't enough to stop his private messages from being discovered.

Update, 4:37 p.m. PT: Updated with more background information.