true, but hey, you're getting something for free, rather than paying for a fully commercial system, so, really ?
To do what you want, you need a lot more sophistication - part of the license key/document could be a 'machine-id', and periodically you could have the client software check that the machine its running on is the same as per the license key (which requires that the license key generator be sent this information when the license is first requested)
further, you could ..
a) ask Oren - see the right hand side panel at
http://ayende.com/blog/[
^]
b) Extend
https://github.com/ayende/rhino-licensing/blob/master/Rhino.Licensing/LicensingService.cs[
^]
btw - you'll never completely avoid malicious users