Q: How do I stop an iTunes website from popping up every minute?

I did actually, my wife has the Pin for Pinterest Application downloaded onto my iMac. It is a little red 'P' in the top right corner of the dektop toolbar. I simply quit that application and it stopped sending me updates for downloading the Pinterest app. Hopefully this solves your problem too. I have left my settings to still open that app everytime I start up the computer, but you could set the start-up options to not turn on the Pin for Pinterest app whenever you start the computer as well.