My ISP is Zen and my package has a 25gb download allowance per month. Recently I've noticed roughly 5gb downloads every Sunday but I couldnt find what was causing these downloads. At first I assumed somebody had hacked my wi-fi but I'm told this is highly unlikely with WPA2/PSK encryption enabled.
This weekend I've been away for 4 days with the PC switched off but the router left on and another 11gb of my download allocation gone. I'm not a techy but I assume that the problem lies at the router.

Any clues as to the problem gratefully received.

The OS is XP and the router is a Draytek Vigor 2820

I would change the wireless password immediatly and even disable wireless when your not using it and see if you still have this problem.

Keep an eye on the Data Flow monitor on the router, which is under the Diagnostics menu, it'll show you which IP is using the bandwidth on your network, but it is realtime.
Otherwise you could use smartmonitor if you can get it to work, that'll give you a log of who has downloaded what.

Thanks for the pointers. As regards changing the wireless pass word I find myself stumped. I can find my wireless network name under the Wireless Lan-General Setup tab but no obvious sign of where the password field lies.

Thanks