Amazon shut down for 2 hours

Apparently Amazon's website was down for 2 hours and as you can see it made a major affect for the company.

So the question is what went wrong? what triggered the problem for a multi-million dollar company.

The company claims it was an infrastructure issue, another theory was a culprit (human error) that caused this or the last theory, possibly an overflow of network traffic or the last thought would be a Microsoft Windows or Linux/Unix server?

Let me know if you have any news on this?