If the defaults don't work, use these methods to regain access:

credentials. Once compromised, the DVR can be used to launch DDoS attacks or spy on the owner's premises.

If you are locked out, "Super Passwords" are often generated based on the system date shown on the DVR screen. Date-Based Generators:

When software methods fail, you may need to go "under the hood." This should be a last resort, as it may involve opening the device.

If default credentials fail, the following methods are typically used to regain access: H.264 Default Password - Google Groups

Remember: If you are buying a used DVR from eBay or a liquidation sale, always assume the previous owner's password is still active. Budget extra time for a hard reset before installation.