WikiLeaks said in a Twitter message on Tuesday that it was under a new cyber attack after a similar incident at the weekend just before the website began releasing secret US diplomatic cables.
"We are currently under another DDoS attack," WikiLeaks said on its official Twitter feed.
DDoS stands for distributed denial of service. Classic DDoS attacks occur when legions of "zombie" computers, normally machines infected with viruses, are commanded to simultaneously visit a website.
Such a massive onslaught can overwhelm servers, slowing service or knocking it offline completely.
A later message on the WikiLeaks twitter said "DDoS attack now exceeding 10 Gigabits a second."
On Sunday, just as it began the release of some 250,000 US embassy cables, WikiLeaks said on Twitter the website had come under a DDoS cyber attack.
But it insisted El Pais, Le Monde, Der Spiegel, The Guardian and the New York Times would go ahead with the publication of the first of such documents even if the WikiLeaks website was down.
WikiLeaks later circumvented the attack by creating a sub-website -- http://cablegate.wikileaks.org -- as its main website -- http://wikileaks.org -- became inaccessible after the attack.
As of 1600 GMT on Monday, both websites were still online.
Explore further: Cyber attacks continue at Twitter, Facebook, LiveJournal