If you are creating an extension for FooBox, or building in support for FooBox in your theme or plugin, the best way to check if FooBox is loaded is by checking if the classes exist.

FooBox Premium

<code>if (class_exists('fooboxV2')) {     //do something if FooBox PRO is running }

FooBox FREE

<code>if (class_exists('Foobox_Free')) {     //do something if FooBox Free is running }