For me it started with learning what I needed to know about security when I worked as a sysadmin. Then when I became a community manager I ended up working for several different cybersecurity companies. I’ve always been fascinated with online security since reading this classic:
https://www.amazon.com/Cuckoos-Egg-Tracking-Computer-Espionage/dp/1416507787
How about you, was it something you always knew you wanted to do, or did you find your way to it?