Dear,
It is important to analyze the security of your site, from what I was hacked in anteiores opportunities. From what I see on-site and zone-h where hackers published the places they entered.
Basically my job would be in two parts, do a pen test and mitigate all vulnerabilities that can be exploited from outside.
Then you analyze malware and shells on the server.
Seguo Once that is protected seguiridad install some tools that will depend on the case.
I welcome your comments.