Locked out of M402dn after upgrade

[AEng3]

This evening, my M402dn had a message about an upgrade being available and prompted me to install the upgrade. I (perhaps stupidly) accepted the prompt and the upgrade proceeded. When it was finished, the display went back to the normal Ready display with the IP address, but now also says Secure in the upper right. Now if I try to access any configuration options from the control pannel I get the message "Menu access is disabled." If I access the printer via the web interface, any of the configuration options prompt me for a username and password. I am certain that I didn't cofigure any username and password when I installed the printer a little over a year ago. Other than the restricted access, the printer seems to be working normally.

Is there a default username and password that I need to use or is there a way to cold-boot the printer to default settings. The only instructions I can find online require using the control panel, which is no longer an option.

Was there a legimate recent upgrade for this printer, or did I clulessly fall for some malware?

[SHThompson]

The default user is usually admin or possibly a administrator on the newer Printers and the default password would be blank, that is to say no password.

[SHThompson]

As a quick follow-up thought it's always a good idea on any new printer to go in and put a password on it using whatever the default username is then it least you have locked it down with credentials you picked.