solve problem of anti spam server linux

hello today we received message alert from OVH of anti spam (from my server start many email of spam) In the past other developer have founded on it, file with code create spam. I think problem of prestashop site, is vulnerability In the emaill received from OVH (company of dedicated server) spoke of an script who create spam. You can solve definitily problem who create damage. We see if no problem, after 10/12 hours from unlock of port 25 for email thank you