I guess the word for it is Unauthenticated

It does start with letter U and it's a 15 letters word. The word unauthenticated fits in to the description perfectly.

• Unauthenticated is not eligible meaning that it's not verified or qualified so to speak.

• It's not secured meaning that without authenticating several owned account, it would be easily hacked. So unauthenticated is not secured in this case.

• Amiss as has the same roots with unauthenticated.