There's a war underway, but you're not likely to hear any shots or see many of the combatants. It's on online war being fought by opposing armies of hackers. The subject? The honor and integrity of WikiLeaks, the much publicized non-profit group that ferrets out and releases government secrets from anonymous sources online.

After the release of the latest batch of documents, U.S. diplomatic cables, the WikiLeaks site was knocked out by repeated denial-of-service attacks. Shortly thereafter, on Dec. 7 (Tuesday), WikiLeak's leader, Julian Assange, was arrested in London after arranging a voluntary meeting with police.

Now, it's apparently time for payback from WikiLeaks' supporters. Cyber attackers claiming support for the beleaguered group have initiated attacks against companies they feel have betrayed WikiLeaks and what they view as the organization's righteous mission. After succeeding in taking down the websites of Visa, MasterCard and others, hackers supporting WikiLeaks tried but failed today to knock online retail giant Amazon.com offline. The group is calling itself “Anonymous,” and its mission dubbed “Operation Payback.” (This is really starting to sound like a Mel Gibson film, isn't it?)

The Amazon.com website did not appear to have experienced any downtime, however, and Anonymous acknowledged defeat on another Twitter feed used by the group to coordinate operations, @AnonOpsNet. “Okay, we have changed our target – the Hive isn't big enough to attack Amazon,” a message posted on @AnonOpsNet said, instructing supporters to switch their focus to the website of Internet payments company PayPal, which is owned by eBay. (The “Hive”? This just gets better and better.)

Why Amazon and PayPal? Amazon last week knocked WikiLeaks off its servers, saying the company had violated its terms of service. PayPal, in turn, has stopped accepting donations for WikiLeaks after the organization's release of secret U.S. diplomatic material.

In an online chat with AFP yesterday, organizers of Anonymous threatened to launch distributed denial of service attacks against any organization they perceive as having an “anti-WikiLeaks agenda.” A denial-of-service attack is accomplished by directing a large number of computers to a certain website at the same time, overwhelming its servers and rendering it unusable while it tries in vain to meet the traffic.

So who is next? In recent days, both Twitter and Facebook have removed accounts being used by the group “Anonymous,” so chances are, these two companies are in for it next, although neither company had anything directly to do with thwarting WikiLeaks' operations, unlike MasterCard, Visa, Amazon and Paypal. Whether the hacker group would succeed in knocking Facebook and/or Twitter offline remains to be seen.