Windows XP is the leader when it comes to rootkits. With 74% of XP machines being infected with a rootkit. Windows 7 only accounts for 12% of infections.
Vlcek assumes that the big reason for this is the extra security built into Windows 7 and the huge amount of pirated copies of Windows XP installed. Many have not upgraded to the higher security of Service Pack 3 for Windows XP due to the fact it does expose that you are running a counterfeit copy of Windows. Microsoft will still serve you security updates as a pirate, but will label you as one in the process.
So, this is your reminder: it is best and most secure to run a legitimate copy of Windows and keep your box patched up with all the required updates for ALL of your software.
Rootkits have become an important part of the most sophisticated malware packages, particularly botnets, because they mask the infection from the user, the operating system and most security software. By installing a rootkit, the hacker insures the compromise goes undetected as long as possible, and that the PC remains available to the botnet’s controller for nefarious chores, such as sending spam or spreading malware to other machines.