The loose-knit group of hackers known as "Anonymous" announced an assault on the Amazon website for 11:00 am (1600 GMT) as part of what they are calling "Operation Payback."
The Amazon.com website did not appear to have experienced any downtime, however, and Anonymous acknowledged defeat on another Twitter feed used by the group to coordinate operations, @AnonOpsNet.
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"Okay, we have changed our target -- the Hive isn't big enough to attack Amazon," a message posted on @AnonOpsNet said, instructing supporters to switch their cyber attacks to the website of Internet payments company PayPal.
In an online chat with AFP on Wednesday, organizers of Anonymous threatened to launch distributed denial of service, or DDoS, attacks anyone they perceive as having an "anti-WikiLeaks agenda."
In a typical DDoS attack, a large number of computers are commanded to simultaneously visit a website, overwhelming its servers, slowing service or knocking it offline completely.
Amazon last week booted WikiLeaks off its servers, saying the company had violated its terms of service, and PayPal has stopped accepting donations for the website behind the release of secret US diplomatic cables.
The Anonymous hackers have also targeted the websites of Mastercard and Visa over the past two days for severing ties with WikiLeaks.
While Anonymous has been launching a wave of attacks, the group has also come in for sanctions itself from Twitter and Facebook.
Twitter suspended an Anonymous account on Wednesday that the group had been using to direct its cyber attacks, @Anon_Operation, but it reappeared shortly afterwards under other names such as @Op_Payback and @AnonOpsNet.
Facebook also removed an "Operation Payback" page.
A Facebook spokesman told AFP the social network takes "action on content that we find or that's reported to us that promotes unlawful activity."
"Specifically, we're sensitive to content that includes pornography, bullying, hate speech, and threats of violence," the spokesman said.
Twitter declined to comment on the move.
Unlike a number of other US companies, Facebook and Twitter have not taken any action against WikiLeaks itself.
The WikiLeaks page on Facebook had 1.15 million fans on Thursday and the group's Twitter feed @WikiLeaks had more than 481,000 followers.
