How to prevent files extraction from an Installer created with NSIS?

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Hi there,

I am pretty happy with NSIS, but i'd wish to avoid to extract the files directly from the Installer EXE. I've serched the Forums and the web without success.

Is it possible to prevent files extraction? if YES, then how?
If NO, then how can I simply encrypt my files inside the Installer EXE using some script lines within the *.nsi file, and WITOUT using a thrid-party software to run properly the Installer?

Thanks in advance,
within