Everytime I try to download a free app it tells me to verify purchase?

Okay so I went to the App Store on my iPhone 5 to try and download a FREE app and when I did a window came up saying "before you can make purchases, you must tap continue to verify your payment info." I thought maybe the app was sketchy so I tried again with a reliable trust worthy free app and this window came up when I tried downloading that app too! Can someone please help me and tell me what this window is and why it's coming up?

Isn't it awful the way they advertise free download and when you do the download they want to know how you are going to pay for it. But when we come down to it they are scams sure you can download it for a month then after you try it here is the bad news. So false advertising is the name of that tune. Just like free virus protection like AVG downloads so if you get a virus ask them for their tech support and they will say I'm sorry I told them sorry don't feed the bulldog if they advertise free virus protection they should be response able to help fix the computer to rid it of that dreadful virus but you get charged by the hour to get rid of the virus. Scams are everywhere so buyer beware.