"Duo’s software hinges on multi-factor authentication, a process to confirm a user’s identity through a second device, like a smartphone, or through a piece of information only the user has. Duo’s technology can also check the health of its customers’ devices, and block access to those deemed risky. Its customers include some of the world’s biggest tech companies, including Facebook, Etsy, Yelp, and Zillow."

https://xconomy.com/detroit-ann-arbor/2018/12...journey/2/