Amazon's UK site suffered a 30 minute outage on Sunday along with the online retailer's Italian, French and German websites. The outage, which happened at around 9:15pm, was first reported by web monitoring firm Netcraft via a Twitter posting.
Initially, it was thought the outage might have been the result of a Distributed Denial of Service (DDoS) attack by a group of online activists that have been targeting websites that have hampered the work of Wikileaks.
WikiLeaks recently published more than 250,000 sensitive cables from the US Department of State. However, MasterCard, PayPal and Visa all announced last week they would stop processing donations to the site because they believed Wikileaks's activities were illegal.
As a result, the Anonymous group took down the websites of the firm in revenge.
Amazon angered the activist after it stopped hosting Wikileaks after the US Homeland Security and Governmental Affairs Committee contacted Amazon "for an explanation" as to why its was hosting the site. The online activists even used Twitter to reveal they planned to target the retailer last week. Anonymous then backtracked on the plans.
However, Amazon said a "hardware failure" was to blame for the attack.
"The brief interruption to our European retail sites last night was due to hardware failure in our European datacentre network and not the result of a DDoS attempt," Amazon said.
The Anonymous group has since revealed it will focus on spreading quotes from the cables across the web, rather than revenge attack.