http://confluence.atlassian.com/display/DOC/Editing+the+Footer - explains how to modify the property files inside of a jar file.
Instead, I just keep it simple, edit ./confluence/decorators/includes/footer-content.vm and comment the first instance of,
$action.getText('licensefooter.community',[$action.getText('url.atlassian'), $action.getText('hitcounter.community'), $license.organisation])<br>
using #* text *#
#*$action.getText('licensefooter.community',[$action.getText('url.atlassian'), $action.getText('hitcounter.community'), $license.organisation])*#<br>