Just to add on to what Mark said, while you are more than welcome to use your software on version 3, it is extremely recommended to upgrade to the latest release of version 4 as version 3 is no longer in development and no longer receiving security releases or bug fixes. Let alone the infrastructure (PHP, MySQL, Apache, etc...) which is required to run version 3 also is no longer supported by their respective authors so it is highly recommended to upgrade our software and your infrastructure so you are not at risk, and receive bug fixes, support, etc...