What version of Evo are you running and are all your add-ons/extras up to date?
That code got into the index.php somehow. Most of these seem to be activated by malicious scripts hidden in the filesystem. Check your files for anything newer than all the rest, or older if you have just upgraded.
Revolution does allow for the renaming of the config.inc.php file, as well as renaming the manager, core and assets directories, and even moving the core outside of the web root. The index.php and other critical files can be set as read-only as well, at least on most system.
It should also be noted that in later versions of Evo, some of the key files are monitored and there is an alert to warn you of changed/altered files. It can only tell you that you've been hacked, not prevent them in the first place.