strange injection in index.php

[eluser]antonyz[/eluser]
Hi,

yesterday one of my clients site was hacked, i didn't develop the site itself and i don't have lots of experience working with codeigniter, but the issue was solved and i need any valuable information to prevent this behaviour in the future.
As i said, i haven't worked much with codeigniter, so i will be thankfull for any help you could provide.

The problem was that the main page loaded blank, the hoster said, there was an error in the main index.php file, once i opened it i saw this code (at the bottom of the file):

http://pastebin.com/9mvk6PzL

What is it? a cookie hijacker, a redirect or what? As i see it is some sort of hash, is there anyway to decipher it?

P.S. codeigniters version on host is : 1.7.1

Thanks in advance.