A TOOL called LOIC turns out to be what's used by the Anonymous group [1, 2], which is linked to 4chan, not Wikileaks. Some people support what they do, but that's another story altogether. To quote:
LOIC (Low Orbit Ion Cannon) is a network stress testing application, written in C# and developed by “praetox”. It attempts a denial-of-service attack on the target site by flooding the server with TCP packets, UDP packets, or HTTP requests with the intention of disrupting the service of a particular host. The program was exploited during Project Chanology to attack Scientology websites, and is currently being used by Operation Avenge Assange (Organized by Operation Payback) to attack the websites of companies and organizations that have opposed WikiLeaks.
Researchers are tracking a new botnet that has become one of the more active DDoS networks on the Internet since its emergence early last month. The botnet, dubbed "Darkness," is being controlled by several domains hosted in Russia and its operators are boasting that it can take down large sites with as few as 1,000 bots.
The Darkness botnet is seen as something of a successor to the older Black Energy and Illusion botnets and researchers at the Shadow Server Foundation took a look at the network's operation and found that it is capable of generating large volumes of attack traffic.