I am trying to implement the following scenario, but not sure how to get it working

Trying to create a corporate website for my company where users are based on regions. Not using portals rather using DNN page security for making the page appear and disappear for the particular user.

Users are logged in automatically based on their IP address to either one of the three listed User Logins

1. US User

2. Europe User

3. Asia Pacific User

These users are already created in DNN and each have a security role by which certain pages are available to a user of a particular region. Also trying to incorporate another combo box feature (looks more like creating a module) where the current user can select  a different region and view the pages of that particular region.

Problem in implementing this is how secure would this be, what are the problems that I am over seeing here and also should there be a web service to subscribe inorder to get the IP address, location of each user trying to access the website.

Any insight on this would help a lot.

Thanks in advance.