Publishing this number is illegal in the USA, because it's something of a commercial secret used to protect copyrights:
09:F9:11:02:9D:74:E3:5B:D8:41:56:C5:63:56:88:C0
or, decimal if you prefer:
13,256,278,887,989,457,651,018,865,901,401,704,640
or get it on a t-shirt (from the USA).
This number is the HD-DVD encryption key. If you know how to do it, it's possible to decrypt HD-DVD disks with this key, making them copyable, downloadable or whatever. As you might expect, there are lawsuits abound over the pond at the moment.
Comments
Moe Wampum has already been selling the HD-DVD hack code t-shirts for 2 days!
http://moeschwag.com/hcrcot.html