Since Windows Vista, a new API called Windows Contacts (WC) was born. It replaces the Windows Address BookAPI.
You can get your personal properties by using the Windows Address Book Editor. It can be opened using “wab” in command line.

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The people from Microsoft decided that the user has to be in full control over the computer. So there is no assured way to make a program user resistant. She can always use TerminateProcess to forcibly kill the process.

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I found this very old but still good article about how to use the Windows API.
These are the subjects:

Part I: The Primer
Windows API calls are just calls to dynamic link libraries
Loading a dynamic link library
Dynamic loading at runtime
Resource only dynamic link libraries
Stack usage and dynamic link libraries
Callback functions
The Hook functions
Data storage in dynamic link libraries
Instanced [...]