I appreciate it as a sign that this was written by hand ;)

This is actually correct English (though admittedly a bit awkward looking). The noun "an" is determining here is "operating system", which of course starts with a vowel. Privacy acts as an part of a compound adjective along with security and focused.

No, it's wrong. The article applies to the entire noun phrase. "A" is correct

If you say "an privacy" it'll sound like English isn't your first language.

I stand corrected, and was actually returning to edit my original post when I saw this. I was always under the impression that the form a or an takes is dependent on that which it determines. Apologies.

Also, it's not even the noun phrase according to the sources I'm looking at (namely Merriam-Webster) state that it is always dependent on the word directly following the article, not even the entire phrase.

[delayed]