You did say that the message was on your desktop, when you went to shut down?
Is that correct?
So, the laptop (MacBook) is simply one of those 7.
Do you have file sharing enabled in your Desktop, too?
Do you NEED any sharing services, other than perhaps printer sharing?
Absolutely, on your desktop, turn OFF all sharing services, except printer sharing, if you need that.
Also, I think you should make sure that no one can connect to your wireless connection, other than what you allow. Any wireless router can block out un-welcome connections, certainly by making sure that security is turned ON (you must supply a password to connect, and you should make sure that the wireless encryption level is at least WPA. WEP, for example, is not a secure connection.
What security level do you have on your Draytek router?
There may be settings in the router to either Allow, or Deny access for specific MAC addresses
So, if you allow your MacBook to connect to the wireless, you then pretty effectively block out anything else on the wireless.
There should also be a DHCP client listing in the router, so you can see by IP address exactly what is connecting to the router.
Finally, do you have other devices, such as XBox, or WII, or other devices such as a so-called Smart TV that also have wireless cards? Do any of THOSE connect to your router, either wirelessly, or through ethernet?