How do i sort out this msn virus?

ok, the other day i got sent a link over msn by my friend which led me to a page telling me i'd been signed out of msn and i had to enter my details in the spaces provided (stupid i know). after i did so, i got a message from my msn telling me that i'd been signed in on another computer...so i signed back in on my own computer, and since then i keep getting spontaneously signed out and then told that i am online on another computer. i tried scanning my computer with virus software but it didnt detect anything, and my friend told me that this particular type of virus works through all your programmes and eventually shuts down your computer. how do i get rid of it??? please help!!!