[shifter]

I'm recieving messages from users who have not added me to their contact list, how is this possible?
If you're using MSN Messenger: right click on the MSN Messenger icon in the system tray, click 'Send an instant message' and choose 'Other'.
If you're using Windows Live Messenger: right click on the Windows Live Messenger icon in the system tray, click 'Send an instant message' and type the contacts MSN (Windows Live) address where you see "Find a contact or number..." and hit enter.

You can also prevent people from using this feature on you. Open up Messenger, go to 'Tools', 'Options', 'Privacy' and click on the check box that says to only allow people in your contact list to send you messages.