The falling-out is potentially bad news for WikiLeaks, whose beleaguered founder remains holed up at the Ecuadorean Embassy in London, where he fled in June in an attempt to avoid being extradited to Sweden over sex crime allegations.
Anonymous is a loosely-organized, often chaotic movement of cyber rebels whose profile grew dramatically after the arrest of Bradley Manning, the U.S. Army analyst who allegedly served as the source of Assange's most spectacular disclosures.
Following the furor kicked up by Assange's leaks, the amorphous collective of online activists has routinely stepped in to support him - either by carrying out cyberattacks on WikiLeaks' opponents, or allegedly by supplying the organization with caches of stolen electronic documents.
When parts of WikiLeaks' website recently disappeared behind a banner asking that users make a donation - a tactic similar to the paywalls of some newspapers online - anger exploded across the Internet, with criticism coming from many who had backed the organization in the past.
"This, dear friends will lose you all allies you still had," said a statement posted by a heavily-followed, Anonymous-linked Twitter account.
The scale of the annoyance among Anonymous supporters was difficult to gauge because the leaderless movement is by its nature hard to get a handle on. But several closely watched Twitter accounts linked to Anonymous expressed anger and unhappiness with the move.
One released a full statement saying that the fundraising campaign was the final straw.
"We have been worried about the direction WikiLeaks is going for a while. In the recent month the focus moved away from actual leaks and the fight for freedom of information further and further while it concentrated more and more on Julian Assange," the statement said. It also expressed annoyance with the 41-year-old Australian's recent meeting with pop diva Lady Gaga at the embassy.
The Anonymous statement said "we cannot support anymore what Wikileaks has become - the One Man Julian Assange show."
WikiLeaks spokesman Kristinn Hrafnsson did not immediately return an email seeking comment. On its Twitter feed, WikiLeaks appeared to shrug off what it described as a "kerfuffle."
"Thank you for drawing attention to our donation campaign while we have high costs in military courts," the organization said - a possible reference to Assange's fear that American officials are preparing to indict him, or have possibly already indicted him, in the U.S.