Felix goes over some basic and essential security configurations for the Raspberry Pi. Modifying the security settings of the Raspberry Pi will allow you to connect to the network more securely. Felix goes over modifying the sudoers file. This file manages how sudo is invoked and what groups or accounts are bestowed with the privileges of sudo. A secure practice is to require an account with sudo privileges to supply a password when calling any program with sudo. Some system administrators like to require anyone logged into the account to also know the root password. The only thing Felix is requiring is for the person to know the passphrase for the account in the sudo group. He also shows you how to create a new key pair. A key pair consists of a public and a private key. He starts by issuing a key gen instruction via SSH. He then shows you how to install and setup fail2ban. Fail2ban is a service that can track failed attemps to the SSH port and if an IP address fails repeatedly, the IP address can be blocked for a period of time, or indefinitely. In the comments below let us know if there is anything related to security that you would like us to go into more detail about.