@merill I have to admit one of the reasons I use the web application for Outlook on my phone is because installing the Outlook app and adding my work account to it would in theory give work access to control (parts of) my phone - which I don't want. I didn't think the authenticator alone would give that level of access to the device though!

Is this likely to just drive more people to switch to using Google's authenticator (or another TOTP app) instead of the Microsoft one? I do anyway, because I was already using it for other sites, and it was easier to have them all in one place. You'd lose push authentications: but I feel safer without those anyway!