dashes vs underscores in URL

In URL rewriting, i am quite confused th开发者_如何学Goat should i use underscore (_) OR hyphen (-) to replace spaces. According to this and this, hyphen should be used. But wikipedia uses underscores like en.wikipedia.org/wiki/Computer_network_programming. so which should be used?

use dashes

read from the matt's blog http://www.mattcutts.com/blog/dashes-vs-underscores/

You can use whatever you want. It doesn't matter (from a technical point of view; there may be other reasons to choose one over the other).