Spam filters can help smooth the waves in your inbox, as long as they are reliable and don’t have too many side effects. We’ll show you what we found when we tested five antispam appliances and two service providers.

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.