Diamond Dan- Welcome to Autpopia!
The scratch is rusting because it's down to bare metal. Even if it looks like there's still a little paint there, you've still compromised the "film build" so now stuff like moisture gets through to the steel. So in this case, it's "surface rust", which I'd sorta consider different from "contamination".
The real way to fix this is to have a paint/body shop repaint the area, but to keep things under control for now, you can arrest/retard the rusting. Clean the area with a solvent (I'd probably use 3M Adhesive Remover, it's great for all kinds of stuff) and then apply a rust converter. I use 3M Rust Avenger, which is available from Griot's if you can't find it anywhere cheaper. This converter/Rust Avenger stuff acts like a primer and it also converts the rust into an inert substance, stopping further rusting. I've even just left this stuff on chips, never painting over it, and had it hold up just fine for many years (didn't looks so hot, but hey, at least it wasn't rusting). But you should probably plan to get it fixed "right" at some point.
