When I attempt to shut down my computer at the end of the day, I sometimes get a message saying "others are logged onto your computer .... are you sure you want to shut down?" My husband and I have networked computers but I get this even if his isn't powered on. Could someone else be logged on and monitoring my email or other activities? It doesn't happen every day.
Thanks.

The only way would be for someone to connect through your wireless router, make sure you have encryption enabled. Often the reason for the another user logged on message is if you have logged on with one account then pressed switch user instead of logging off, then when you shut down the other user you were logged on with is still logged on.