You have to be root to load modules in the kernel so your system can't be compromised because of modules. Modules aren't directly related to security but as they are executed in the kernel space, they have full control over the running system. Therefore, modules can intercept system calls, access all files and kill any process. The lcap utility offers an easy access to this file. Modules are part of the Kernel and can take control or monitor the running system.
Modules can create or intercept system calls.
Only the system adminstrator's imagination is a limit. Check the parameters to certain system calls. Log all the commands of special users. This makes it possible to detect someone trying to exploit a buffer overflow on your system. Here are 3 modules that give examples of what it is possible to do to with modules.