Fix Linux Iptables and Locate Server Outgoing Ddos Vulnerability

Server: Linux. Centos Version 5.11. PHP Version 5.2.17 NOTE: Server is running older versions of Centos and PHP. This is required for proprietary software we are running and can not be changed and updated. The server hosts a number of database driven sites. We do not use a control panel of any sort. All site information is stored in MySQL databases. We are also running mydns. Our ISP has informed us that this server is being used for outgoing dos attacks. There are no external clients on this server, so it can't be a client initiating the attacks. I have attempted to restart apf and I am seeing a number of errors: iptables: Unknown error 4294967295 Further, IP's that have been manually added via apf -d are still being allowed through. Chkrootkit did not turn up any issues. service iptables restart produced the following messages Flushing firewall rules: [ OK ] Setting chains to policy ACCEPT: filter mangle nat [ OK ] Unloading iptables modules: [FAILED] Applying iptables firewall rules: [ OK ] Loading additional iptables modules: ip_conntrack_netbios_n[ OK ] So, I am looking to have iptables fixed and ddos vulnerability shutdown. If bidding, please respond with a brief history as to why you are the right person to fix this. Thank you.