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Effective October 28, 2019 Duo Security will be transitioning to Cisco's Privacy Statement. View the Duo Privacy Data Sheet.

A method of monitoring and recording the flow of data between two communication points while not altering or otherwise disrupting it. Because of its passive nature, sniffing allows hackers to gain information directly, or assess the technical details of a network and plan for a future attack, while garnering less suspicion than a more overt approach.