The WikiLeaks website said it came under a forceful internet-based attack Tuesday morning, making it inaccessible for hours to users in Europe and the United States.
The site appears to have recovered from the attack with the help of Amazon.com Inc.'s U.S.-based server-for-rent service.
Late Tuesday morning, web traffic to the site was handled by Amazon Web Services.
The site, which made available a trove of U.S. diplomatic documents Sunday, said in a Twitter message that it was under a "distributed denial-of-service attack," a method commonly used by hackers to slow down or bring down sites. WikiLeaks didn't identify the attackers.
The site, which is devoted to releasing anonymously submitted documents, also came under attack Sunday, but Tuesday's attack appeared to be more powerful.
Calls to Seattle-based Amazon.com were not immediately returned. Bahnhof, a Swedish Internet company that has been involved in hosting WikiLeaks, had no immediate comment on Tuesday.
In a typical denial-of-service attack, remote computers commandeered by rogue programs bombard a website with so many data packets that it becomes overwhelmed and unavailable to visitors.
Pinpointing the culprits is difficult.
Large attack effort
WikiLeaks said the malicious traffic was coming in at 10 gigabits per second on Tuesday, which would make it a relatively large effort.
According to a study by Internet security company Arbor Networks, the average denial-of-service attack over the past year was 349 megabits per second, 28 times slower than the stream WikiLeaks reported.
Sunday's attack didn't stop the publication of stories based on messages leaked from the U.S. State Department in several major newspapers. WikiLeaks had given the media outlets prior access to the diplomatic cables to publish in conjunction with their Sunday release on its site.
The cables, many of them classified, offer candid, sometimes unflattering assessments of foreign leaders, ranging from U.S. allies such as Germany and Italy to other nations like Libya, Iran and Afghanistan.