If you've setup your own passwords for the Cisco 675/678 and forgotten them, this procedure will help you reset them. CAUTION: This will also erase your router configuration!
Connect your 675/678 to your PC via the management cable (originally supplied with the router - connects between the Cisco 675/678 and your PCs serial port)
Login to the router (using Hyperterminal or other serial port based terminal application)
Note: connect using 9600 baud, 8-N-1, no flow control
Remove, then restore power to the Cisco 675/678
As soon as the Cisco 675/678's red ALARM light comes on, hit Ctrl-C a few times to enter ROM monitor mode
Enter the following two commands:
CBOS# es 6 (erases sector 6)
CBOS# rb (reboots 675/678)
Once the unit reboots (you may need to manually power cycle the router) you can reenter your user info