I have a pc and laptop which I use with a wi-fi router for connecting to the internet. I have password protected the network using the WPA pre-shared key but on veiwing my history of ADSL Bandwidth Usage I find that there is ingoing and outgoing useage during the Off Peak (1 am to 6 am) period. As I never use the internet during this period and and nobody else has access to my computers how can this happen. Both pc and laptop are switched off at night.
In your router config manager, Turn 'mac address control' on in 'allow mode' and configure so only your 2 systems can access the router. click start-run type ipconfig /all to find mac addresses of your network adapters and allow access to those only.
Some (maybe all) routers allow you to configure the allowed MAC list from the router's web pages. You just connect the relevant PCs and then go to the routers pages and pick the MAC addresses (and hence PCs) that you want acess permitted for.
Note that wireless laptops typically have two MAC addresses - one for the wireless and and one for the wired.
BTW, your router's log may also shed some light on whether anyone else is accessing it.