Last release compatible with PHP 5.3 and Joomla! 1.6 to 3.3 (inclusive).. If you are on PHP 5.4+ / Joomla! 3.4+ please install Akeeba Backup 5.
This version is compatible with Joomla! 1.6, 1.7, 2.5, 3.0, 3.1, 3.2, 3.3, 3.4 and 3.5.
Please note that we do NOT recommend using Joomla! 1.x / 2.x or 3.0 to 3.3 inclusive on production sites due to major security issues. Support for these old versions is intended to give you the option of taking a full site backup prior to upgrading to the latest available Joomla! release.
If you have Joomla! 3.4 or later and PHP 5.4 or later please use Akeeba Backup 5.x. This version of Akeeba Backup (4.7.x) will only receive very irregular security fixes but NO bug fixes or new features. This version of Akeeba Backup is only published for people managing older sites so that they can back them up before upgrading them. Any other use is strongly NOT recommended!
The minimum required PHP version is 5.3.03. All versions of PHP from 5.3.03 onwards are supported, including 5.4, 5.5, 5.6 and the just released PHP 7.0. The component will not work on PHP 5.2 or earlier and will, in fact, refuse to install on it. We'd like to remind you that Joomla! 3.4 and earlier does NOT support PHP 7. Joomla! 3.5 (currently in beta) does support PHP 7. Akeeba Backup will work just fine in a Joomla! 3.5 site running on PHP 7.0.
Note: there is no such thing as PHP 6. PHP versions jumped from 5.6 to 7.0. Why? Well, it's a long story. TL;DR: It doesn't have to make sense, just accept it.