Inducted into the National Cyber Security Hall of Fame in 2012, she is now Emeritus Distinguished Professor of Defense Analysis, Naval Postgraduate School.

She joined SRI International as computer scientist from 1983 to 1987, working on the first intrusion detection system and on database security.

After a stint as principal software engineer at Digital Equipment Corporation's Palo Alto Systems Research Center (1987-1991), she returned to academe as chair of the Computer Science Department at Georgetown University.

With husband Peter in 1997 she edited Internet Besieged: Countering Cyberspace Scofflaws, a comprehensive collection of essays on cyber security.

She testified multiple times before various congressional subcommittees studying technology,[8] infrastructure,[9] intellectual property,[10] and cyberterrorism.

"A Lattice Model of Secure Information Flow" presented in 1976[13] provided a method for controlling access to data which is still used today.

SRI's Intrusion Detection Expert System (IDES)[14] ran on Sun workstations and considered both user and network level data.

[26] With L. Scott, Denning wrote two papers on using Global Positioning Systems for geo-encryption to enhance data security.

[27][28] Although she remained a technical expert, Denning's interests evolved to consider legal, ethical, and social issues.

Denning was widely criticized for one what could characterize her inept role in NSA's controversial Clipper chip initiative to give the government authorized access to encrypted private communications through a key escrow system.

Her testimony helped lead the government to drop charges against defendant Craig Neidorf,[38] who had taken an electronic 911 directory across state lines.