This function has been completed and can be tested at
You must be registered to see links
.
How it functions:
On register you assign a pin, it is encrypted with MD5(or if you move to the cms users just enter it upon login).
If you login from a different IP than you usually use it will redirect you to the verification page to enter your pin.
Users will be able to request a pin reset via account settings when this is finished.(Update - this is now working with an "Are you sure" message using an HTML onclick)
If you want any changes made please let me know.
I have decided that I will not release it as a separate addon as I think it would be too much messing around for people to edit the core classes to get some parts of it to work and some of it may not have my "header.php" file which is in all my revisions and may be annoying for some people to do it properly.
May do it in a different way if I want to do "stand-alone" addons in the future.