BT have realised that using admin as a password on their routers is a dumb idea. You ought to change it anyway, but as a security measure they are updating the firmware to change the default password to the router's serial number.
My HomeHub just got updated, and as a result has been reset to the factory defaults. That meant setting up my wireless again, but it also meant that the portforwarding that I had done for WinMX was erased from the memory. I had to do it from scratch again.
Just a heads up in case it happens to you.