Most anti-rootkit scanners (ARKs) do not work on 64-bit systems. Why?
64-bit drivers need to be digitally signed. Due to the architecture in 64-bit windows, rootkits are not seen as often in 64-bit machines so they are less prone to that type of infection. As such, it doesn't really matter if ARKs do not run on 64-bit since that OS is more secure than a 32-bit system. However, Sophos Anti-rootkit
supports 64-bit platforms.