There seems to be a myth that Microsoft limits security updates to genuine Windows users. So who gets Windows Security Updates?
Not only do all security updates go to all users’ systems, but non-genuine Windows systems are able to install service packs, update rollups, and important reliability and application compatibility updates. In addition, the users of non-genuine Windows systems can also upgrade a lot of the other software on their computer. For example Internet Explorer 8 has numerous security- oriented features and improvements, and it is available to all users.
This isn’t to say that all updates are available to non-genuine PCs. Other value-adding updates and software may or may not be blocked, at Microsoft’s discretion. On Windows Vista, available updates can be accessed through the Windows Update control panel. On Windows XP, a non-genuine Windows system can access updates through Automatic Updates, but they cannot get to any of the optional updates which are only available through the Windows Update and Microsoft Update websites.
Keeping a machine up to date is one of the first steps in helping ensure that they remain reliable, compatible, and safe from threats when they are online. Some of the most famous incidents of malicious software infection have come after security updates were publicly available from Microsoft – Blaster, Zotob, Conficker and Sasser, just to name a few.
Source: The Windows Blog.