With expertise spanning red team operations, adversary simulation, penetration testing, incident response, and threat intelligence, Pieter Ceelen brings a unique perspective that combines offensive security techniques with real-world attacker behaviors. He began his career at KPMG’s cyber division in 2008, conducting penetration tests, technical security advisory, and adversary simulation before working as an independent consultant from 2013 to 2016. As an independent consultultant he used his offensive experience in a defensive role as a threat hunter and incident responder.
Pieter co-founded Outflank in 2016 to deliver sophisticated red teaming and attack simulation services. His background in attack simulation and threat hunting enabled him to replicate the tools and techniques employed by actual threat actors, making security assessments highly realistic and effective for testing organizational defenses.
Outflank debuted its tool suite, Outflank Security Tooling (OST), in 2021 and was acquired by Fortra (owner of Cobalt Strike) in 2022. In 2024 Pieter began managing the Cobalt Strike team and spearheading the collaboration between Outflank OST and Cobalt Strike.