Separately, a group of hackers calling themselves Anonymous Operations said they would attack PayPal, not Amazon.com, about an hour after an attack on Amazon was due to start.
"We can not attack Amazon, currently. The previous schedule was to do so, but we don't have enough forces," they said on Twitter.
Anonymous Operations released a do-it-yourself hacking tool earlier Thursday so supporters could make their own computers part of the attack.
The Amazon.com attack was supposed to have started at about 11 a.m. ET.
So far, PayPal appears to be operating normally. The site has been attacked, which has slowed it down but has "not significantly impacted payments," PayPayl's Anuj Nayar told CNN.
Amazon.com has massive server capacity -- much more than that of Mastercard or Visa -- in order to handle the holiday e-commerce rush. Its server infrastructure ensures that a massive traffic spike can't take site down, whether it comes from a hacker-led attack or genuine shoppers.
Anonymous Operations released the hacking tool on Twitter and called for followers to translate it into other languages.
Hackers have been targeting websites of organizations they see as hostile to WikiLeaks and its Editor-in-Chief Julian Assange, who was arrested in London this week on allegations unconnected to the website's publication of secret documents.
Amazon used to host WikiLeaks' website in the United States, but shut it down last week, saying it had violated their terms of service by publishing material it did not own and which could cause harm.
PayPal stopped handling donations to WikiLeaks last week.
The United Nations Commissioner for Human Rights said Thursday that pressure on websites to cut off WikiLeaks could violate the site's right to freedom of expression.
