I go to a forum which uses vBulletin 3.8. When I log in, I use firebug to see what cookies were set. I see these cookies:
__utmb, __utmc, __utma, __utmz, bbsessionhash, vbseo_loggedin, bbpassword, bbuserid, bblastactivity, bblastvisit
They all had a value set, and the domain was identical.
__utmb, __utmc, __utma, __utmz, vbseo_loggedin, bblastactivity, bblastvisit