After hitting Paypal, Mastercard, and Visa, pro-WikiLeaks forces may hit the United States Senate website with a denial-of-service attack next.

According to a poll set up by the ad-hoc group, Operation Payback, the Senate could be their next target. It leads voting ahead of Re-attacking Mastercard, Re-attacking Visa, Sarah Palin's website, and Authorize.net. Out of a total of 1179 votes cast (as of 5:22 pm), 445 of them went to attacking the Senate website.

This iteration of Operation Payback formed in response to companies like PayPal, Visa, and Mastercard cutting off WikiLeaks from their services. It is composed of members associated through the loose network of people known as Anonymous, which specializes in denial-of-service attacks, among other general mischief. For more on how the group organizes itself, The Economist has a great piece called, "The 24-Hour Athenian Democracy."

It's important to remember that these denial-of-service swarms are not attacks or "hacks" in the sense that they break or break into the computers running a website. Rather, they clog up the pipes leading to the website so that others can't access it. In that sense, they are non-destructive attack. Perhaps the best off-line analog is picketing, although obviously it's hard to do a one-to-one mapping of the digital onto the real.

At least one Dutch teenager has been arrested in recent days in connection with Anonymous' activities.

And for clarity's sake we should also note that Anonymous is not affiliated with WikiLeaks in any way. The latter organization issued a statement neither condoning nor condemning the attacks.