It's very easy to have someone snooping or listening for MSN chat conversations on your network, Your computer security depends not only on the user name and password but on many other factors, including and not limited to Spyware, and other malicious programs, not to mention if you are using an un-encrypted wireless connection where ur chat, passwords, and other data can be snooped easily over the air..

I suggest you have an expert to assess your PC/Network environment.. and if security is a serious issue for your laptop/pc/network usage then an expert assessment is a must..

;)