Security fix on existing MODX website

I have a website running on MODX platform with some custom coding on Kohana framework and it has some security issues which has to be fixed. Some malicious code has been injected recently and it started sending a huge amount of spam and it's been blocked by the provider. I have a clean backup of the website and I can easily restore it but I'm looking for someone who can locate and fix security issues so it doesn't happen again. I can provide server log files and access to MODX, FTP and MySQL as well.