DIAGNOSIS That's usually caused by the infrared (IR) LEDs reflecting off of something very close to the lens. Common culprits are a cobweb, a bug sitting on the dome, or even a buildup of pollen or dust that's invisible in daylight but glows under IR light.
FIX You need to give the dome a thorough clean, paying special attention to the ring around the lens where the IR LEDs are housed. 1) Follow the steps above to disable motion alerts first. 2) Unplug the camera if you can safely reach the plug. 3) Use a can of compressed air (like for cleaning keyboards) to blast around the lens ring and dislodge any tiny debris. 4) Then, wipe the entire dome gently with a microfiber cloth. Plug it back in and check the night vision view.
IF THAT DIDN'T WORK If the spots are still there after cleaning, look at what's in the camera's field of view. Is there a shiny, reflective surface like a window, a metal sign, or a car bumper within a few feet? The IR light is bouncing off that and back into the lens. You may need to slightly adjust the camera's angle to avoid that reflection.
HEADS UP Don't use the compressed air can upside down, as it can spit liquid that could damage the seals. Hold it upright, use short bursts, and keep it a few inches away from the camera.