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[eluser]WanWizard[/eluser]
Care to explain what it is that makes this secure?

A quick glance of the code shows that you have removed the most secure part of CI's session library, which is the encrypted session cookie.
Instead, you rely on $_SESSION, and I assume PHP's native session cookie as well (although I don't see a sess_start() call anywhere, it needs auto start needs to be configured too?), which is very insecure!