The outage underscores the pitfalls inherent in Internet commerce.
"We're sorry! Our store is closed temporarily. If you enter your email address, we'll notify you as soon as we reopen. Again, our apologies for the inconvenience," read a notice posted to the site yesterday afternoon.
As a way of apologizing for the inconvenience, Amazon said it would offer customers an additional 10 percent off books they purchase by midnight tonight, according to an email message sent to users.
A company spokeswoman explained the cause of the closing as "an internal technical problem. There's no problem with the database or the security."
Online book sales is one of the fastest growing categories in e-commerce.