The camera was given a public IP address or placed in a DMZ without being behind a VPN or secure gateway.
Accessing or interacting with private security systems without authorization may violate privacy laws or computer misuse acts in various jurisdictions. If you own such a device, it is recommended to set a strong password and disable anonymous viewing in the network settings.
The device was installed with "anonymous viewing" enabled by default.
The accessibility of these feeds is rarely intentional. It typically occurs because: