There was an addon that logged when a user had multiple user accounts and logged each one and when they "switched" WW95 beleive was the original creator and I helped support it for awhile but I do not beleive it was ever updated to the latest version of UBB as I am not licensed for it. Might want to try searching...
Donate to UBBDev today to help aid in Operational, Server and Script Maintenance, and Development costs.
Please also see our parent organization VNC Web Services if you're in the need of a new UBB.threads Install or Upgrade, Site/Server Migrations, or Security and Coding Services.