Shopping website Amazon went offline for a brief period, prompting fears it may be the latest victim of sabotage from cyber attacks by WikiLeaks supporters.
But the company denied that "hacktivists" were responsible, attributing the disruption to technical issues instead.
A spokesman said: "The brief interruption to our European retail sites last night was due to hardware failure in our European data centre network and not the result of a DDoS (distributed denial-of-service) attempt."
Amazon.co.uk was unreachable, while the company's French, German and Italian domains were also experiencing problems.
But after about half an hour on Sunday night the UK site was working again, a relief to thousands of Christmas shoppers.
Hacktivists originally suggested they may be responsible for the site going down. Anonymous, a group of online hacktivists who support the whistle-blowing website WikiLeaks, has claimed responsibility for a series of DDoS attacks in the past week.
The attacks have disrupted the websites of companies including Visa, Mastercard and PayPal by bombarding them with millions of visits in revenge for withdrawing WikiLeaks' services.
A message on a Twitter account used by the activists, Anonops, on Sunday night read: "We cant confirm anything because we'll lose our accounts again. Be alert and you will realize." The message was deleted minutes later.
An earlier post which quoted Abraham Lincoln read: "Those who deny freedom to others deserve it not for themselves."
Several accounts attributed to Anonymous and its campaign, dubbed Operation Payback, have been suspended over the attacks.