The only way to get rid of that is to zero out /var/wtmp and log out of all vertial terminals. You could also reboot, but why bother when you can fix it without doing that? The magic command is "cat /dev/null >/var/wtmp." Catting /dev/null over any file will make it empty but leave its ownership and permissions intact, so this is the best way to empty out a file that the system relies on. Good luck.
