System will work, but it will gradually get less and less secure, which can get quite bad.
There is an insane amount of ways to break Windows XP and even Windows 7, it's basically script kiddie's level of knowledge.
And there are real exploits out in the wild that target such systems specifically - while the pool of potential victims is smaller, they're very easy to target unless they are competently firewalled.
The most beautiful thing about this program is that it would work.
Various bit flips will once lead to all numbers being in the correct order. No guarantee the numbers will be the same, though...