Shadowbox – preventing the window underneath from scrolling

I’m a big fan of the web-based media viewer application Shadowbox and use it where necessary. However in a recent project I noticed that the contents of the window over which the shadowbox overlay opens, remains scrollable using the mouse wheel.
I wanted to prevent this behaviour and as usual I performed a Google search. I found many questions on it, but no answers. So I looked into it myself and managed to come up with something that works and is quite easy really.
