CIA Director's affair exposed through email
The discovery of an extramarital affair between CIA Director David Petraeus and his biographer, Paula Broadwell, culminated in his resignation. What is interesting from a technical perspective, is how the affair was exposed by the discovery of email messages stored in Petraeus' personal Gmail account.
Many observers expressed surprise that the head of the CIA and an intelligence officer were so easily busted. Indeed, while there are many secure methods of communication, the appeal of email probably lies in its simplicity and ease of access. In a way, this mirrors how most corporations conduct their business today--using emails that may be accessed from systems that are not properly secured.
Finally, it's interesting that no email messages were actually sent or received; as described in a report on The Washington Post. The messages were instead saved as draft emails for the other to log in to read. The initial investigation, in which the FBI looked into threatening emails from Broadwell to another woman, were sent.
The report noted that this "draft" trick has achieved notoriety as a tactic of terrorists who are wary of email interception. In this instance though, the FBI clearly knew to go straight to the "draft" folder upon gaining access to the email account.