It'd be easy to move the hidden elements on to the screen when the user clicks the submit button, so they'd be filled in and the form would then be submitted, and the information 'phished'.
The solution to this problem is to inform the user which fields will be completed by autofill, with a "not currently shown" highlight on any fields that are currently off the screen so the user understands what's happening.
The solution to this problem is to inform the user which fields will be completed by autofill, with a "not currently shown" highlight on any fields that are currently off the screen so the user understands what's happening.