If you are using IE explorer to read your email and you exit via
the upper right hand X only your acct. stays logged in for 2 hours.
and yes it is possible for someone to access your acct durning that time frame if they so wanted.
It is always good practice to "sign out" of each opened window
even if you have already signed out from the messenger service.
Change your password on a regular bases (once a week) and if
someone is still getting into your email acct. then contact MSN and
they will provide you with more help.

when you are done using your msn service clear your history trial, that way you can check to see if your acct has been accessed again afterwards.
(unless they do likewise

)