Blatant newbie question - killing a session

Hi, this is my first question to the list and ... Yes I'm a newbie, verrry wet behind the ears. I am trying to set up a secured site under IIS. I have done pretty well by my standard to get to where I have. Authoursed users can access the site, unauthorised ones get sent elsewhere. So, I am now up to testing the various security combinations and its driving me mad that the session persists when I'm testing bad logins. How or where does one set up a "session extuinguisher"? After one two or n attempts I want to kill the entire session and start afresh - note this is in testig only, the way it works now is great for live. Tia Bruce