error in login?

im not sure whats wrong, but ive been able now to log in a few times withiout havin to give up name and password. doin this form my own comp i end up logged in as myself, which of course wouldnt happen if i was at another comp i hadnt used before, but it would mean that anyone else using a comp which you logged into would be able to go and write under your account without having to log in...

just thought i would mention it, somehting similar happened on another forum some time ago