Your CCTV is connected via an Internet connection.
I'll recommend to isolate the network devices from the Internet before continuing.
This is covering only basic steps, I recommend to get the instruction manual for the CCTV and read it.
- Enter the administration section of the CCTV recorder/DCR/NVR by entering your admin account name and password.
- Go to the admin setup of the CCTV. Search for overlay and verify if the hacker inserted text on the overlay feature, if you don't use overlay, disable it.
- Then check each camera name tags in the admin section. Change the text if it was hacked.
- Change the password for the CCTV DVR/NVR/Camera, I bet it was never changed. Write the password down and store it in a safe place.
- Last option: If you can't find the place do a factory reset of the DVR/NVR/Camera. (Do make a backup before a factory reset to an external device if possible).
- Once the factory reset is done, you will have to reconfigure the recording options for each camera.
- Last point after the factory reset, change the admin password.
Are there other devices sharing the Internet connection with the CCTV?
If this answer is YES, then check them for hacker breach.
- I'll recommend to increase the security on the Internet Router.
- Any device sharing the Internet with the CCTV should be checked for breaches and made secure.
- Speak to your ISP and ask for assistance if you have a fixed IP address to your CCTV system. Ask them for advice. Layer 7 routers are more expensive but more secure.
- Load all updates for any devices!
Get an IT security expert to assist you with the breach if necessary.