In addition, you'll now get text messages whenever changes are made to your account, so you'll get a heads up if someone else is tinkering things in there. The company says it already uses a machine learning model that predicts whether it's the true owner or a hijacker who's trying to log in based on locations and IPs. If the system thinks it's a hijacker, it will require additional info.

However, account takeover is one of the biggest problems on the internet today, since hackers have more and more password dumps from massive security breaches to consult. If their targets' passwords aren't there, they can also turn to phishing or infecting people's computers with malware. Airbnb must have felt that its machine learning model isn't enough anymore and added the extra layer to keep interlopers out.