Since the begining of Unix history security has always been an important issue. The earliest versions of Unix had many security holes that were exploited easily. More recent versions of Unix have come along way towards being a more secure operating system. Most of the time a default, out-of-the-box Linux or *BSD install is fairly secure without any modifications. Of course this doesn't mean that you shouldn't do whatever you can to make you box more secure!
This section of the TFUG helpdesk is designed to be a place where the new-to-unix user or the new-to-security user can learn about different ways to make sure that their boxes are as secure as they can be. This is in no way meant to be an all inclusive site for Unix security. If you find any incorrect info or think that I am leaving something out please feel free to contact me.
Generally the best security policy is one of "least privilege". That is, you only give others the minimum amount of access to your box that is necessary for them to do what they need to do. Improving the Security of Your Site by Breaking Into it is an older paper that everyone should read.