We’ll show you a custom solution for moving spam to a separate folder and adding new spam signatures to SpamAssassin.

Track down and expose intruders with the versatile admin tool lsof.

Backdoors give attackers unrestricted access to a zombie system. If you plan to stop the bad guys from settling in, you’ll be interested in this analysis of the tools they might use for building a private entrance.

Users log on to services such as SSH, ftp, SASL, POP3, IMAP, Apache htaccess, and many more using their names and passwords. These popular access mechanisms are a potential target for brute-force attacks. An attentive bouncer will keep dictionary attacks at bay.

If you are looking for an extra layer of remote access security, try single-packet port knocking.

The ancient Linux permission system is often insufficient for complex production environments. Access Control Lists offer a flexible alternative.

SELinux provides a safer system through the powerful concept of mandatory access controls.

Services that require a username and password for login are potential targets for dictionary attacks. Sshutout and Fail2ban introduce time penalties for invalid attempts.