Ralf Spenneberg has used Linux since 1992 and worked as a system administrator since 1994. During this time, he worked on numerous Windows, Linux, and UNIX systems. Starting in 1998, he has been working as a freelancer in the Linux/UNIX field. Most of the time he provided Linux/UNIX training. His specialty is network administration and security (firewalling, VPNs, intrusion detection, forensics). He has published several German books on VPN, IDS, Firewalls, and Mandatory Access Control. His two current companies, OpenSource Training and OpenSource Security, offer training and support in the Network Security field. OpenSource Training was the first Sourcefire Authorized Training Center worldwide. OpenSource Security is providing pentesting services for governmental and commercial clients.