Oscommerce CRE Security Fixes Needed

We have a couple websites that use Oscommerce CRE Loaded. About 2 weeks ago a hacker installed rootkit into our server. Our server techs told us they believe the hacker gained access by a security hole in Oscommerce. We need someone experienced with OScommerce CRE security patches to check our website and install necessary patches. This should be an easy job for an experienced person.