http://www.usa.canon.com/cusa/consumer/products/cameras/slr_cameras/eos_5d_mark_iii?pageKeyCode=prdAdvDetail&docId=0901e02480538fc7Affected Product
Canon EOS 5D Mark III Digital SLR Camera
*Products whose sixth digit in the serial number is 1 or 2 are affected.
For example, “xxxxx1xxxxxx” or “xxxxx2xxxxxx” ([x] represents any optional number.)Support
Under almost all shooting conditions (including dark environments) this phenomenon will not affect your captured images. However,
if you would like Canon to inspect your camera, we will provide this service free of charge upon request beginning in mid-May. Please contact Canon using the information below to request service.