I applied online. The process took 1+ week. I interviewed at HackerOne (San Francisco, CA) in July 2016
Interview
I met with 4 different higher-ups during the 2 hour interview process. I spent 30 minutes with each. The first interviewer was the chief of staff, second was the CFO/COO via Video Chat, 3rd was head on the engineering team, and the last was the head of customer support.