Can I pack a cardboard box as checked luggage?

As mentioned in another question, I'm planning on traveling with a desktop computer as checked baggage. After considering the options, I've decided to take it in its original cardboard box (used for shipping), making sure to pad everything inside very well.

What should I do to securely prepare the box before checking it in? Some suggestions others have given me so far:

Spray paint the box black so it's not obvious there's a computer inside.
Wrap the entire box with duct tape to reinforce it.
Use tape to seal the "hand holes" on either side used for carrying the box.
Run packing tape around all the edges to reinforce the box.
Write "FRAGILE" on multiple sides of the box.

Best Answer

London Heathrow has a service wherein they'll essentially wrap your box in green saran wrap (a plastic film). The idea is that it will be immediately evident to any thieves that a box has been tampered with, and thus they had be awfully sure that they want to break in before attempting.

This answer about wrapping your luggage at the airport will have more about that.