In an attack called "Operation: Payback," a group of online activists called "Anonymous" apparently plotted a "distributed denial of service" attack on the site, blocking its services to many users, The Guardian reported Wednesday.
The hack is the latest volley in the cyberbattle over WikiLeaks, after MasterCard announced Monday it no longer would process donations to the whistle-blowing site, claiming it was engaged in illegal activity.
The group has been targeting commercial sites that have severed relationships with WikiLeaks, The Guardian said. The Swiss bank PostFinance was targeted by Anonymous after the financial institution froze WikiLeaks founder Julian Assange's account, and the group pledged to strike Paypal, which stopped processing payments to WikiLeaks.
The actions and reactions come after WikiLeaks recently released more than 250,000 classified U.S. State Department cables that were published in several newspapers. Assange was jailed in London after being arrested on a sexual assault warrant from Sweden.
The hack was confirmed on Anonymous's Twitter page Wednesday, where a post read, "Group that took down Swiss bank has now taken down MasterCard.com"
Several other posts on the Twitter page read, "Operation: Payback (is a bitch)."
Other operations that suspended dealings with WikiLeaks include Amazon, Visa and EveryDNS.net, a domain name service.