Modules are easily used to intercept the kernel. Modules are a good design for the linux kernel to make the linux kernel more modulized and more felixible. But after the modules are inserted into the kernel, it will be part of the kernel and can do what the original kernel can do. Therefore some unfriendly code could be written as a module and inserted into to the kernel. The code can even redirect the system calls and act like a virus.
Processes are unprotected.
Certain processes, such as a web server daemon, which are vulnerable to the attack of hackers. We must have a secure kernel and then build our secure system on top of it. This is what LIDS does. The Linux Intrusion Detection System is a patch which enhances the kernel's security. Ituses and extends the system capabilities bounding set to control the whole system and adds some network and filesystem security features in kernel to enhance the security.