Why do different windows open onto other windows?

Kernel Patch Protection: The Kernel Patch Protection feature (also known as "Patchguard") on 64-bit versions of Vista that locks down the OS kernel has been criticised by computer security company McAfee who claim that since PatchGuard also prevents third-party security companies from getting inside the OS, they cannot activate crucial security measures in their software to protect the OS from intruders. Microsoft's argument is that this will keep miscreants out of the OS and prevent the incidence of attacks, and it is something for which customers have been asking. Firewall maker Agnitum and others have argued that the Patchguard can be circumvented by hackers and that some security software makers must use similar methods. McAfee has also stated that Vista will be even less secure than previous versions of Windows. However, security vendor Kaspersky Lab claims that it is not more difficult in Vista for anti-virus software to work, and that it would not make sense for Microsoft to stop working with security companies because it would make their system more vulnerable to attacks. Sophos adds that Microsoft does not need to open PatchGuard for third party developers, instead, they should use the APIs Microsoft supplies them.