For whatever reason imaginable, Apple ID of some users have been locked ever since earlier today. Rumours on the Internet are that it may be the work of a large scale attack on Apple’s security systems. Thankfully, in most cases answering a security question and entering a trusted phone number for validation is enough to regain access.
We will let you know more as soon as there is any official information. For now, though, do not panic and know that you are not alone.