Instituting ‘Defense in Depth’ for PCI Compliance on a Linux Platform

“There are several possible points of entry into any system.
Entry can be physical, by someone actually accessing the hardware
of the system. Then, entry could be through the network. Entry can
be through a process or through a kernel operation. And finally,
entry can be through the file system. Now, instituting defense in
depth means that you defend each layer from a possible

“Your first step is to restrict access to your main server by
physical means.”