In an email sent out to developers today, Apple has announced that starting on February 27, all developer accounts will require two-factor authentication to be enabled. After that date, developers will not be able to sign into their Apple IDs without two-factor authentication (via MacRumors).
For those who aren’t yet aware, two-factor authentication is an extra layer of security designed to ensure that you’re the only person who can access your Apple ID, even if someone knows your password. Once you enable it, a verification code from a trusted device will be required for logging on to your developer account.
So, if you are an iOS or a Mac developer but do not yet have two-factor authentication enabled for your Apple ID, you should set it up before Feb. 27. For instructions on how to enable it for your account, visit this page.