He is credited with a number of innovations in firewalls, including building the first Internet email server for the whitehouse.gov domain,[1] and intrusion detection systems.

Marcus Ranum was born in New York City, and graduated from Gilman School in Baltimore, Maryland before attending Johns Hopkins University where he obtained a Bachelor of Arts in Psychology in 1985.

He left DEC to work for Trusted Information Systems (TIS) as chief scientist and development manager for Internet security products.

Three months after that IPO, Ranum formed his own company, Network Flight Recorder (NFR), and served as CEO for three years before stepping into a CTO role.

Marcus has co-authored a series of "Face Off" articles with Bruce Schneier, which have appeared approximately bi-monthly in Information Security Magazine since July, 2006.