A number of people on Twitter and Reddit are reporting that they are waking up this morning to their Apple ID being locked. The issue, which has an unknown origin, requires iPhone users to answer security questions and enter a trusted phone number to resolve. In some cases, users may have to reset their Apple ID password.
Apple, for security reasons, will lock accounts if too many attempts on a wrong password are used to unlock an iPhone or iPad. Why this issue is happening randomly is a mystery and Apple has not confirmed anything as of yet.