In 2021, Cobalt Strike is appearing in Proofpoint threat data more frequently than ever. Cobalt Strike is a legitimate security tool used by penetration testers to emulate threat actor activity in a network. However, it is also increasingly used by malicious actors – Proofpoint saw a 161 percent increase in threat actor use of the tool from 2019 to 2020. This aligns with observations from other security firms as more threat actors adopt hacking tools in their operations.