When your first receive the device, it is set with the factory default access credentials:
After logging into the device for the first time, the administrator is prompted to change this password before accessing the web GUI. You must define a strong passwords to prevent the device from being compromised. Weak passwords, like universal passwords, represent one of the most exploited attack vectors for compromising a device.
Guidance on best practice on passwords can also be found in the following documents:
At minimum SonicWall recommends that the password meets the following requirements