This is a modified WSO PHP shell backdoor that maraudes as a 404 in order to try and hide. On top of that the backdoor is probably backdoored.
You can download it from the following link: https://packetstormsecurity.com/files/download/137439/404.txt
Source: https://packetstormsecurity.com/files/137439/WSO-Shell-Variant-Using-A-404.html

