Security of replaced HD

I have just had a crashed HD replaced under warranty, but under the terms of the warranty, the old HD had to go back to Apple. Since the computer would not even boot (even with an external drive or an installation CD), I was unable to erase it which made me wonder, how does Apple handle the possibility of sensitive information on returned HD's?

I don't know how they handle a hard drive that was removed and replaced under warranty. I guess you'll have to assume they will either destroy the drive or send it to the junk pile. A good reason never to store sensitive data on your hard drive without encrypting it first.