Joomla malware/spam issue

We are having an issue with a joomla (version 3.3.6) website causing malicious files to be uploaded via what we assume is a security vulnerability. We have changed the FTP and other passwords multiple times but the malware keeps being uploaded (in the form of PHP malware and javascript injections in existing files). We would like you to examine the joomla site (you will be given limited SSH and file access) and tell us where it\'s happening and how we can fix it permanently. If you require anything more than SSH and file and log access, please let us know upon accepting the job. You will be given the domain in question when we select you for the job.