Many DVRs are installed by electricians or security contractors with little to no networking expertise. Their goal is to get the camera recording and the feed visible on a monitor. Connecting the device to the internet for remote viewing is often done with a "plug-and-play" mentality, bypassing firewall configurations or security protocols.
: Turn off "Universal Plug and Play" on your router to prevent the device from automatically opening ports to the internet. CCTV Camera Pros are currently exposing your devices? intitle dvr login