FYI....this was posted on the B&H site regarding Canon's T6i camera:

Product Advisory: In some units of the EOS Rebel T6i white spots may exist on the optical layer which may result in the appearance of dark circular patterns on the capture image under certain shooting conditions. Potentially affected units include cameras with serials numbers of "XXnnnnnnnnnn" in which XX is 01 or 02. These cameras will be inspected and repaired free of charge by Canon USA.