Sigma news: Potential AF issue with recent zoom lenses

Sigma has discovered that there may be an autofocus issue with some of its recent zoom lenses:

• --- APO 50-500mm F4.5-6.3 DG OS HSM
  --- Serial Numbers between 10633051 and 10972000
• --- APO 120-400mm F4.5-5.6 DG OS HSM
  --- Serial Numbers between 10574001 and 10972000
• --- APO 150-500mm F5-6.3 DG OS HSM
  --- Serial Numbers between 10674301 and 10972000

 Details of how they'll help you get it fixed available here.