Hello Marco
If you are trying to log in to the "shell" / "terminal" of the virtual machine through your virtualbox terminal then you need the default credentials for "SSH / Linux Users" in that link. Let us know how you go.
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Please note: this is for logging in to the the virtual appliance interactively, i.e. on your VM console or via SSH. This is not the password for the Web GUI!
login.tiff
I'm trying to start with virtualbox, NMIS8 which also includes open audit. But I do not understand what are the credentials. Ones that I found at the following link https://community.opmantek.com/display/NMIS/Default+Credentials+%28Passwords%29+for+NMIS8+VM
do not work