Is it possible to disable Net Passport?

​ My grandson set up an e-mail address in MSN Explorer. I very seldom use this to access the internet, usually IE. Quite often when I open IE, it usually opens to the net passport page with that e-mail address and then prompts for the password. A couple of MSN sites that I visit are members only sites and will not let me on until I type in my e-mail address and password. It's an irratating hassle that I'd rather not have to deal with so often. I've tried to find this net passport entry in the registry, but haven't had any luck. What's the best avenue to rid myself of this e-mail address of his? I deleted the account in the MSN hot mail folder, but still getting this logon hassle. ​