Update 3:22 p.m.. For details, check our . Updated 12:43 p.m. PDT with further details, including partial site recovery.
Amazon.com was inaccessible to many U.S. visitors for more than an hour and a half Friday.
The site went offline completely by 10:21 a.m. PDT, but efforts to restore the site appeared to be taking effect about noon, said Keynote Systems, which monitors Web site responsiveness. As of 12:45 p.m., the site was working intermittently, with many product pages functioning but others still broken.
"At noon PDT, we started to see the site getting better," said Shawn White, director of external operations for Keynote. "We are seeing about 70 percent availability."
One-off outages are no fun, but sustained problems can be a serious problem. eBay suffered outages in 1999 that outraged users and sent the stock down, and even a backup system didn't ward off more problems in 2002.
And for major commerce sites, the problem can have ripple effects. Both Amazon and eBay provide a commercial foundation used by many partners and entrepreneurs.
Based on last quarter's revenue of $4.13 billion globally, a full-scale global outage would cost Amazon more than $31,000 per minute on average. For North America, it would be more than $16,000 per minute. (To be fair, those figures don't include revenue from other sources such as search or contextual advertisements or Amazon Web Services.)
Of course, money lost can be money gained for a competitor. A Sony PlayStation 3 promotion with the Metal Gear Solid 4 game went on sale at 10 a.m. PDT, according to some CNET News.com readers. Another reader went to BuyDig.com to buy a birthday present.
"Http/1.1 Service Unavailable" was the message that appeared when Amazon customers across the country attempted to use the site.
Representatives of the company haven't responded to requests for comment.
Amazon Web Services unaffected
It appears Amazon Web Services such as the S3 storage and EC2 computing services still are functioning, at least for some customers, though the AWS page at Amazon.com isn't working.
"S3 and EC2 continue to function for us as normal," said Don MacAskill, chief executive of photo-sharing site Smugmug. Mashery.com CEO Oren Michels, who uses AWS for several functions and who has several customers who use AWS, reported no problems Friday.
Customers who need to get to their AWS pages can follow a direct link, Amazon said.
The security group WebSense concluded the Amazon problems are "not security related" as far as it's aware. Arbor Networks Chief Technology Officer Jose Nazario was more cautious, though: "I've got nothing on it as to why or what happened. I'm not sure if it's an attack or service outage via failures on their end or what."
What's your theory on the cause of the Amazon.com outage?
News.com staff writers Greg Sandoval, Rafe Needleman, and Robert Vamosi contributed to this report.