After using default credentials, scan your network. Infected DVRs often show:
If you enter the wrong password seven times consecutively, the account will lock for 30 minutes or until the system reboots. How to Reset a Forgotten Multistar Password multistar dvr default password work
The phrase "default password work" implies not just finding a static string, but understanding it may fail (prior owner, firmware version, lockout) and how to bypass those blocks. After using default credentials, scan your network