said by garethccc:
I looked at his wireless network settings and the correct password was stored for our network. I would have thought this impossible if I hadn't seen it with my own eyes.
Any password is replaced with a series of dots or asterisks in any respectable operating system. Can you post a screenshot of what you are talking about?
Anyway did you have to change the password on your own computer to access the internet? If yes, someone had to do the exact same on his computer. If no, your router has a mode which does not need a password.