From the original Marathon Trilogy Box Set License: (c) 1997 Bungie Software Products Corporation All Rights Reserved. PO Box 7877, Chicago, IL 60680-7877 Marathon is a trademark of Bungie Software Products Corporation All other trademarks are the properties of their respective owners. From http://trilogyrelease.bungie.org/faq.html Q: Hey, I thought Marathon needed serial numbers! A: The versions released with the Trilogy Box Set were stripped of the serial number code. These will work fine - as long as you're not trying to play with folks who are using older versions. Q: Wow... can I do whatever I want with this stuff? A: NO. Bungie still holds the copyrights to these files. They're allowing them to be distributed for free (mostly because you can't buy them any more) - but they're still Bungie's intellectual property. You can't, for example, sell them.