For a "what not to do", have a look how (the CEO of?) FTDI responded after they were caught intentionally "bricking" chips that were detected as counterfeit by the Windows drivers.
Go out right now and get the book "Crucial Conversations". It is BY FAR the best book I've ever read on this kind of thing. It is simultaneously the best relationship book I've ever read and the best business book I've ever read. It goes through the basic principles for handling these situations in an easy to understand way.
* Actually apologize in a human way
* Show empathy by identifying the impact of what happened to customers (not your impact internally)
* State action items that you've created, even if they are just in 'evaluation' state
* Indicate that the specific incident in question is being handled outside of this forum
* Take responsibility for things even if you shouldn't "have to"