Did you know that if your wireless connection is not secure, that if somebody uses your bandwidth for some unsavoury task, it is you that is responsible for it!
West Mercia Police are currently on a crack down on this, I'm sure other police forces will act similarly.
It's simple just secure the wireless connection. Details will be in the manual, if it isn't or you can manage it yourself then why not contact a local IT company to come and do this for you.
It is also worth noting that you should change the default password on the admin account for your router.