Today, both from my iPad and my Mac Mini, I was asked to verify my account information in iTunes (app store on the iPad) when I tried to purchase an app. In both cases iTunes became unresponsive - on the iPad it left a shadow of the information window on the screen, on the mini hitting the continue button just seems to do nothing. In both cases I could exit iTunes/AppStore and use my machine normally, but the purchase didn't happen.

Now I'm suspicious - anyone else have this happen to them - verify credit card info and/or unresponsive iTunes/AppStore?

I haven't faced such things happened during purchasing.

I will suggest you to create virtual Credit Card (VCC) on your Credit card for online payments as safety option.

iTunes has been tightening up security requirements on accounts as has been reported by several Mac sites. The dialogue you are seeing may be in relation to that.

Apple improving iTunes account security with stricter requirements (http://www.appleinsider.com/articles/12/04/12/apple_improving_itunes_account_security_with_stric ter_requirements.html)