Rootkits are used to hide malware on a computer system. This paper describes the cat-and-mouse game between the Microsoft Corporation and the developers of malicious rootkits. Microsoft introduced several anti-rootkit features in its Windows Vista and 7 operating systems; however, rootkits such as Alureon, Popureb and Mebromi managed to break through these defensive measures. Microsoft plans to beef up its security in Windows 8 with a more secure booting process and a redesigned heap manager.