icloud sign in suddenly appearing; hack or spam?

[Peteyer]

All of a sudden, on my iphone 4, I started getting a box appearing on my screen that says that says, "sign into icloud" Undedrneath that it says " Enter the apple ID password for (my email)." Then it has a place to enter apssword, and underneath I can click on cancel or OK. If I press cancel, it appears again 5 or 10 seconds later. I do not know why it suddenly started appearing, I never have signed into cloud on my phone, and I have never seen that before. I cannot figure out how to shut it off. I do not want to enter my icloud password in case it is a virus or whatever. What to do? I tried turning it off and on, and doing the reset. It is making me crazy. I cannot even dial a whole phone number without the thing appearing and my having to click on cancel three or four times.