I was really taken in by the title and devoured the article. I must admit I got lost half way through and would not dare implement this in case I did something incorrectly (which could actually open up new - even easier - avenues to intruders).
Perhaps you could have added a little "test routine" at the end?
If you ever find the time to revise this article, I suggest you give a somewhat more thorough explanation of some of the steps you outline, so that readers with a limited knowledge of UNIX can still follow you!
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