The new Apple 27-inch iMac has been plagued with problems since it release, one of the issues was in its Flash performance. That issue had already been fixed with an update that was only supported for those running Mac OS X 10.6.2, but a new update is now available to download.
Firmware update 1.0 will help to improve the issues with the ATI Radeon HD 4670 and 4850 graphics cards, meaning that the screen will no longer be corrupted or flicker. We are not certain if the issue has been solved fully or not, comment below and let us know if the problems have now been solved.
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When you do update your Apple 27-inch iMac, make certain that you do not disturb the computer or power down during the update process. If this happens, then you iMac could fail to start up, something that you do not wish to happen.
Apple do state that this update should solve the corruption or flicker, if it fails to do so then contact AppleCare ASAP, or an Apple Authorized Service Provider. For more information on how to update your device, visit Apple Support.