A scary development in rootkits:
Rootkits typically modify certain areas in the memory of the running operating system (OS) to hijack execution control from the OS. Doing so forces the OS to present inaccurate results to detection software (anti-virus, anti-rootkit).
For example rootkits may hide files, registries, processes, etc., from detection software. So rootkits typically modify memory. And anti-rootkit tools inspect memory areas to identify such suspicious modifications and alarm users.
This particular rootkit also modifies a memory location (installs a hook) to prevent proper disk access by detection software. Let us say that location is X. It is noteworthy that this location X is well known for being modified by other rootkit families, and is not unique to this particular rootkit.
Now since the content at location X is known to be altered by rootkits in general, most anti-rootkit tools will inspect the content at memory location X to see if it has been modified.
In the case of this particular rootkit, the original (what’s expected) content at location X is moved by the rootkit to a different location, Y. When an anti-rootkit tool tries to read the contents at location X, it is served contents from location Y. So, the anti-rootkit tool thinking everything is as it should be, does not warn the user of suspicious activity.
Source: Forged Memory