Duo Security

Founded in 2010 in Ann Arbor, Michigan, by Dug Song and Jon Oberheide — a security startup outside Silicon Valley, which back then was distinctive in itself. Their bet was that MFA hadn't caught on because it was a chore, so Duo Push replaced six-digit codes with a notification: tap "Approve" and you're in.

It worked, arguably too well. The same ease is what "MFA fatigue" exploits: an attacker holding a stolen password fires off prompts until the victim taps yes just to make the phone stop buzzing. Duo later added number matching. Cisco bought the company in 2018 for $2.35 billion and made it the centrepiece of its zero trust offering.