I've been having similar problems. Have a sneeking suspicion that someone has been pilfering my internet download capacity. Blown 20GB download limit within 2 weeks even with free download feature from midnight to 8am. Not likely!!
Downloaded ZANSZOM network monitoring tool and found 6 other machines on my network. Changed the security password on my router but my laptop can still connect even with the old network password. Also been getting a bubble saying that my network is "unsecured". Laptop is running Xp that is all up to date with patches.
Just an aside, I'm have been trying to change the wireless network password on the laptop. When I check the WPA2 option I can't update the password. When I use the WPA-PSK I can change the password but when I click OK it reverts back to the old password. The funny thing is that the laptop is still on the network despite having the wrong security password.
Go figure!!