This is how i see it. I'm not a license expert, but this software has NO licensing at all. Don't?
It can be treated as Freeware because it's free to use.
It's free to edit/modify/share, but you can edit only unencrypted part, the addition code part, menu building. module addons.
This is not GPL, is not Opensource and is not under other license. If you can break that encryption, there are no prohibitions published into webpage nor attached license document. (watch
http://centos-webpanel.com/terms-of-service)
When the publisher finally put the license file over a version, that applies to that version, so you can use AS YOU WANT the older versions, like the actual.
I wanna recommend developer to put ANY license, because code encription is only time based. Time based mean that someday one guy will break encription used (Zen i guess, not ionCube).
Regards and thank you for this software.