In a new support document published today, Apple announced the opening of a AMD Radeon 6970M video card replacement program for certain 27-inch iMacs.
The machines with the affected video cards were sold between May 2011 and October 2012, all with Intel Core i5 processor quad-core 3.1GHz or Core i7 quad-core 3.4GHz. The problem causes the computer screen to appear distorted, white or blue with vertical lines, or to be dark.
If you have such an iMac and have already noticed the problem, contact Apple technical support, take your machine to an Authorized Service Center or schedule a visit to a Genius Bar at an Apple Retail Store near you.
Affected iMac owners have up to three years after the retail date of the computer to request a free replacement of their video card.