In response to a common VoIP security question, Digium provides ten ways to protect your IP PBX from hackers.
1. Use a private network and exclude international calls from this network
2. Ask your Service Provider to help restrict calling
3. Use a firewall from the inside
4. Verify IP addresses
5. Never use the root user and disable login as such
6. Create strong passwords and change frequently
7. Close all ports that are not in use
8. Run any susceptible services (for example, SSH) on non-standard ports
9. Ask IT experts to protect platforms
10. Never step learning about new security threats and protections
If this has piqued your interest or concern about VoIP security, check out VoIP Security: The Risks and How To Prevent Them.