Diagnosis
Dust and oils have accumulated on the polycarbonate lens dome. It is not glass and scratches very easily.
How to Fix It
Power off the camera by unplugging it. Use a clean, dry microfiber cloth designed for eyeglasses or camera lenses. Gently wipe the dome in a circular motion. Do not apply pressure.
If That Didn't Work
For stubborn smudges, lightly dampen a corner of the microfiber cloth with distilled water. Wipe gently, then immediately dry with the clean, dry section of the cloth.
Heads Up
Never use window cleaners, isopropyl alcohol, compressed air, or paper towels. These contain chemicals or abrasives that will permanently cloud or etch the plastic lens.