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>