Petraeus Used Email Trick to Contact Mistress Paula Broadwell

Former CIA Director David Petraeus and his ex-mistress Paula Broadwell reportedly used a common email trick in an attempt to hide their extramarital affair. It is one that is often used by spies and terrorists.

The pair shared a Gmail email account and regularly composed explicit draft emails for each other but made sure not to actually send the messages. By saving draft messages for each other, Broadwell, 40, and Petraeus, 60, were able to communicate without a trail of internet-protocol (IP) addresses, according to CBS News.

Broadwell, a married mother of two and a self-proclaimed "over-achiever," first began working with Petraeus as a Harvard University researcher after meeting him in 2006. She later wrote his biography, "All In: The Education of General David Petraeus," which was published in February.

She reportedly began having an affair with Petraeus, the long time husband of his wife Holly and a father of two, in 2011. Their affair was later uncovered by the FBI after Tampa socialite Jill Kelley complained to authorities after receiving threatening emails from Broadwell.

Petraeus, who served in the military for 37 years and was sworn in as head of the CIA in September 2011, cited his inappropriate relationship with Broadwell as the reason for his resignation on Friday.

"I showed extremely poor judgment by engaging in an extramarital affair. Such behavior is unacceptable, both as a husband and as the leader of an organization such as ours," Petraeus said in his letter.

Kelley, who was reportedly told to "stay away" from Petraeus in Broadwell's emails, was initially suspected to be Petraeus' second mistress. New reports, however, have tied her to General John R. Allen, a married father of two and commander of U.S. and NATO troops in Afghanistan.

Authorities reportedly also found sexually explicit emails exchanged between Kelley, who has an unpaid position as a social planner for MacDill Air Force Base, and Allen, 58. The married mother of three has since hired Monika Lewinsky's crisis manager and disgraced former Senator John Edwards' attorney Abbe Lowell to represent her.