The method Gen. David Petraeus and Paula Broadwell used to communicate secretly on the Internet is commonly used by terrorists and is not the most secure option available, a security expert said.

"It is possible he is just an administrator and not savvy about the latest technology out there," said Thomas Avery, a computer forensics expert with Precision Discovery.

 Petraeus and Broadwell reportedly used the "dropbox" technique to transfer messages between them. This method eliminates the need to send or transmit email, which can be easily traceable by investigating agencies. The dropbox method allows the author of a message to simply save it and logout without the need for transmission. The intended recipient of the information then logs into the same account reads the "draft" message and deletes it.

 "It is not a simple technique to uncover unless you have direct knowledge it is occurring," Avery said.

 It is not yet completely clear how the Petraeus/Broadwell messages were discovered, but Avery said there is a more secure way to get the job done.

 "Use those free new mail services. Everything is encrypted inside those mail services," Avery said.

 A search of "free encrypted email" yielded several companies that offer such services.

 Avery believes if Petraeus and Broadwell had used one of these services, they're intended-to-be-private messages would not have been discovered.

Certain investigative techniques can reveal whether a user has visited an encrypted email website, but in most cases cannot reveal what information was transmitted or to whom that information was sent.