App store charge free application

I don't know what's happened with my iphone, for every new application, even those free ones, App Store asks to enter my credit card information. If I disagree and hit "Cancel", installation process is interrupted and I can't install any application, even free one.

Sometimes, because I really need that application like I have just downloaded IKEA catalogue, the App store charged me 1usd??? especially that I'm installing only free applications.

Am I missing some significant change to the App Store or this is some kind of bug or virus? Is there anything I can do in this situation? How can I install a free application from the App Store, without having to share my credit card information with Apple?