There was nothing terribly sophisticated about the denial-of-service attack executed by the activist hackers at Anonymous to temporarily knock out the website of Americans for Prosperity, the conservative advocacy group backed by billionaire brothers David and Charles Koch.

But the senior execs at Georgia Pacific and other corporate holdings controlled by the Koch brothers ought to be very nervous. Anonymous, best known for similarly crippling websites of firms hostile to WikiLeaks, says it has begun actively probing for network weaknesses in Georgia Pacific and other Koch brothers' holdings.

Should the activist hackers succeed in cracking into any of the Koch brothers' corporate networks, Anonymous could solidify its emerging persona as a digital-age Robin Hood, says Josh Shaul, chief technology officer of network security company Application Security.

"These guys have so much attitude and spunk," says Shaul. " Anonymous is coming out of its shell and seems to be saying, 'Hey, we'll be the voice of the people, we'll be the Robin Hood fighting for the poor against the powerful.' "

In this statement, Anonymous accuses the Koch brothers of "fabricating grass-roots organizations and advertising campaigns to sway voters based on their falsehoods." The statement concludes:

Anonymous hears the voice of the downtrodden American people, whose rights and liberties are being systematically removed one by one, even when their own government refuses to listen or worse -- is complicit in these attacks. We are actively seeking vulnerabilities, but in the meantime we are calling for all supporters of true Democracy, and Freedom of The People, to boycott all Koch Industries' paper products. We welcome unions across the globe to join us in this boycott to show that you will not allow big business to dictate your freedom.

The group's highest-profile hack to date shows what it is capable of. On Feb. 5, a group of five elite hackers gained deep access to data intelligence firm HBGary, defaced and damaged most if its systems, and stole 77,000 e-mails from the Google Enterprise cloud-based service used by the company.

Upon being made public on the Internet, the stolen e-mails were pored over by reporters and activists; they revealed stunning details of how high-stakes, corporate-backed disinformation campaigns get birthed.

Click here to read about the pivotal role a 16-year-old girl played in that hack. The lightning rod in that caper -- HBGary Federal CEO Aaron Barr -- on Monday announced his resignation. Barr will go down in tech history as the disinformation expert who stirred Anonymous into a higher gear -- by bragging that he had identified the group's leaders and planning to expose them on Valentine's Day at the Security B-Sides conference in San Francisco.

Though corporations have spent billions shoring up network perimeter defenses, determined hackers routinely gain deep access into corporate systems. They do so by combining simple social-engineering trickery with proven hacking tools.

We recently published this news story about how one cybergang stole more than $50 million by setting up an elaborate series of stings of European companies participating in Europe's carbon-credits exchange. Another gang got deep into Nasdaq's Directors Desk cloud collaboration tool for senior executives, where they lurked for more than a year before recently being detected.

The activist hackers at Anonymous have demonstrated knowledge and skills of the techniques used by top hacking groups that concentrate on breaking into corporate networks for profit.

"They better be concerned," Shaul says of the Koch brothers. "What Anonymous is saying is, 'We're getting ready to execute whatever attack we can, so you better be worried. In the meantime, we're going to be a big pain.' "

Update: 5:50 p.m Eastern. A Michael Goldfarb called Technology Live and identified himself as a spokesman for Koch Industries. Goldfarb requested to go off the record for a "substantive discussion." We declined. The caller declined to comment on the Anonymous attack.