This information is logged in /etc/utmp and /etc/utmpx. In 5.0.4, this information is cleared when the system reboots. For earlier releases, edit /etc/bcheckrc as follows. You will see the first of the following three lines already there; add the other two below it.
/bin/su bin -c "/etc/devnm / 2>/dev/null" | /etc/setmnt [ -w /etc/utmp ] && > /etc/utmp [ -w /etc/utmpx ] && > /etc/utmpx
Also, "cwtmp" ftp://ftp.armory.com/pub/scobins/cwtmp is a freely available utility that clears stale logins.
Also available for Linux: ftp://ftp.armory.com/pub/linux/cwtmp
Got something to add? Send me email.