Software Versions and why they are important
Half the battle of security is simply ensuring your software is up to date. Software is versioned so that you can tell at a glance if you are running the current release.
Zen Cart version
The version information for Zen Cart, PHP and MySQL article explains how to determine your Zen Cart version.
The version information for Zen Cart, PHP and MySQL article explains how to determine your PHP version.
PHP’s Version Support Policy will tell you if your PHP version is still supported. Remember: old versions are not PCI compliant, and are not deemed “secure” if they are out of the maintenance period.
You will want to run the latest PHP version which is appropriate for your Zen Cart version. See Server Requirements for running Zen Cart.