Windows Live Web Authentication does not provide site owner any information except an anonymous 128-bit (32-digit) ID, so when user sing-in to site for first time, no information is available except this ID. SharePoint may display System Account instead of user name too.
In Shetab Windows Live Authentication for SharePoint, user will prompt to set his information including his name if he didn't set it yet when he sign-in. He will see his name in all site including Welcome message as soon as he set his name. User need verify his email address if email validation is turned-on.
See Also
Why Windows Live Web Authentication does not provide site owner any information except an anonymous?