543398 Need My Site Scanned and Secured against Malware

Someone keep attaching malware files to my images on my server that allows them back door access. I have twice found MAL/PHPShell-A attached to certain images on my server by loading the site to my computer periodically and doing a virus scan. In addition, in the past, there were SQL injections on some of my php pages. A developer I regularly contracted supposedly fixed the SQL injections but the malware came back recently. Even though I deleted the files in question, my site is still being compromised. Someone is still accessing my site as they are starting to erase sensitive data and playing around with member profiles I need this addressed ASAP. I am running Unix server with GoDaddy and using php and approx. 5 My SQL databases. Must have proven experience in dealing with internet security threats. 1) Scan entire server files for any malware and SQL injections 2) modify necessary files and make coding more secure 3) change permissions of files/folders to tighten security 4) once done securing, let me know so I can change all database passwords and FTP access (which I do everytime I encounter the malware) 5) specifically tell me exactly what you did, what files were modified, and how you made the site more secure