9. Kernel Callbacks And Timers

The Windows operating system allows a driver to register a callback routine, which will be called when a particular event occurs. For instance, if a rootkit driver wants to monitor the execution and termination of all processes running on the system, it can register a callback routine for the process event by calling the kernel function PsSetCreateProcessNotifyRoutine, PsSetCreateProcessNotifyRoutineEx, or PsSetCreateProcessNotifyRoutineEx2. When the process event occurs (starts or exits) the rootkit's callback routine will be invoked, which can then take necessary action such as preventing a process from launching. In the same manner, a rootkit driver can register a callback routine to receive notifications when an image (EXE or DLL) gets loaded into memory, when file and registry operations are performed, or when the system is about to be shut down. In other words, the callback functionality gives the rootkit driver the ability to monitor system activities...