REPEAT: this problem is NOT in iTunes, it is a problem with iOS 7. Because the alert appears when you connect your phone to a computer that is switched on, but not even running Windows or OS/X, let alone iTunes.
In fact, the ONLY time this issue does NOT occur, is when you plug into a computer that IS running iTunes under Windows or OS/X, that you have previously trusted.
And if I reboot my "trusted" Windows computer while my iPhone/iPad is connected, the moment the power cycles (during the reboot), up pop the trust messages again.
If I UNPLUG my devices before rebooting Windows, and WAIT until Windows is fully running - then no message. If I plug in too soon, before Windows has loaded the Apple drivers, up comes the message.
It's a friggin' pain - and IS NOT ANYTHING TO DO WITH ITUNES.
Brian