You never worry about your site security until after your site has been hacked for the first time.�A�û�����߱z���������w���A���ܱz����������A�w�Q�妺�A���Ĥ@���C It is always a moment of truth, when you first realize how vulnerable you (your site & your data) truly are.���l�׬O�@�ɨ�A�u�z�A��z�Ĥ@����{�h�򪺯ܮz�A�A�]�z�������P�z���ƾڡ^ �A�u���O�C You have probably dozens of scripts running on your server ranging from weblog software, comment form, maybe a CMS like Mambo or Joomla, not to mention your home-grown scripts.�z���i��X�Q�}���B��b�z���A�Ⱦ��W�A�q�իȳn��A��ת��Φ��A�i��O�ӭM�趯�ʤ��|���Ҫi��joomla �A��N�קA���g�ͤg��}���C Have you ever had them audited?�z���S���J��L�L�̼f�p�H Do you always keep updating them whenever a new release is available?�A�`�O���_��s�L�̨C��@�ӷs�����O�i�Ϊ��H Do you run all your applications and scripts in chroot jail?�A�B��z�Ҧ������ε{�ǩM�}���bchroot�ʺ��H Do you regularly check for rootkits?�A�O�_�w���ˬd��rootkit �H The answer to most of the above is probably no.���פW�z�j�����i��O�S���C The truth is that any of them can lead to your site and data being compromised.�ƹ�u�۬O�A�L�̥���i�ɭP�z�������M�ƾڨ��l�`�C In this context an intrusion detection system can provide you early warning when something goes wrong so you can fight it.�b�o�譱���J�I�˴�t�Υi�H���z���Ѧ����wĵ�A��@�ǿ�b���̡A��z�i�H�������C Let's look at Samhain, a popular intrusion detection system.��ڭ̬ݬ�samhain �A�y�檺�J�I�˴�t�ΡC

Samhain is a multiplatform, open source software (GPL) for centralized file integrity checking & host-based intrusion detection on POSIX systems (Unix, Linux, Cygwin/Windows�K). samhain�O�@�Ӧh���x�A�}�񷽽X�n��] GPL���^������󧹾���ˬd�ΰ��D�����J�I�˴�W��POSIX�t�Ρ]���Ω�UNIX �A Linux �A cygwin /�bWindows �K �K �^ �C It has been designed to monitor multiple hosts with potentially different operating systems from a central location, although it can also be used as standalone application on a single host.���w�Q�ΨӺʴ�h�ӥD���i��b���P���ާ@�t�ΡA�Ѥ@�Ӥ�����m�A���M���]�i�H�Q�Ψӧ@���W�ߪ����ε{�Ǥ@�ӳ�@���D���C

Samhain can be used standalone on a single host, but its particular strength is centralized monitoring and management. samhain�i�H��W�ϥΤ@�ӳ�@���D���A���S�O���O�q�A�N�O�����ʱ��M�޲z�C Samhain can be extended by writing modules. samhain �A�i�H����g�@�Ҷ��C The client (or standalone) part is called samhain, while the server is referred to as yule.�Ȥ�ݡ]�οW�ߡ^���@�����A�O�ҿת�samhain �A�ӪA�Ⱦ��O�Q�٬��t�ϸ`�C Both can run as daemon processes.��̳��i�H�@���u�@�i�{�B�檺�i�{�C

The bottom line is that intrusion detection systems (Samhain or otherwise) are as much a necessity for web servers as virus checkers for individual PC's.���u�O�J�I�˴�t�Ρ] samhain�Ψ�L�覡�^�@�ˡA���n�������A�Ⱦ��@���f�r���Ѥl�A���ӤH�q�����C