Scores of websites and Internet services like Foursquare and Reddit crashed or had limited availability Thursday because of problems at a data center run by Amazon.com.
The problems revealed widespread reliance on Amazon Web Services, which rents out computers and data storage on a self-service basis over the Internet.
AWS is generally considered reliable because it uses vast numbers of computers, spread out in different data centers, making Thursday's failure unusual.
Amazon said the trouble started early in the morning at a data center in Northern Virginia but provided no details.
The problems were ongoing Thursday afternoon.
Foursquare, which lets people tell others where they are with the help of cell phone GPS chips, was still experiencing technical issues.
HootSuite, which provides a "dashboard" for social media like Twitter feeds, was down completely, as was questions-and-answers site Quora.
Reddit, a "social news" site owned by Conde Nast Digital, was in "emergency read-only mode."
Amazon.com Inc. is the leading provider of this type of "utility" computing, where customers pay only for the computing power and storage they need. Anyone with a credit card can begin using it. Competitors include Rackspace Hosting Inc. and Microsoft Corp.'s Azure platform.
Seattle's Amazon has big plans for its Web Services. CEO Jeff Bezos said last year that it could eventually be as large as Amazon's retail business.