Over the weekend, the Honker group attacked US sites leaving pro-China messages on many and disabling others. The homepage of the Honker Union of China hosts a three-page list of all the sites it has claimed to have attacked.
As Chinese and US diplomats work to re-establish normal relations in the wake of the spy plane row, hackers in both countries are continuing the conflict in cyberspace.
Responding to a wave of attacks by US hackers, a group of Chinese hackers are embarking on a campaign to deface as many American websites as possible.
So far, the attacks seem to be limited to replacing legitimate webpages with pro-China messages.
But the FBI and web security organisations are warning that more serious attacks could be on the way.
Online attacks
Soon after the diplomatic row blew up over the mid-air collision of a US spy plane and a Chinese military jet, American hackers started attacking Chinese websites in their own form of protest against China's actions.
Since the 1 April incident, US hackers have reportedly been carrying out 40-50 attacks a day on Chinese websites, and defacing or hijacking those found to be vulnerable.
Websites that watch and report on hacking activity say up to 300 Chinese websites may have been hit. Many of the attackers left behind racist messages or images accusing the Chinese Government of cowardice.
Now, a Chinese hacking group called the Honker Union of China has said it is retaliating against these attacks. The word "Honker" is Chinese for "red user". A message on the Honker website said: "We are obligated to strike back with utmost force after such provocation by American hackers."
Conflict escalates
The group declares its aim as "safeguarding the motherland's reunification, defending state sovereignty, unanimously resisting humiliation from overseas, and deflating anti-Chinese arrogance".
Over the weekend, the Honker group attacked US sites leaving pro-China messages on many and disabling others. The homepage of the Honker Union of China hosts a three-page list of all the sites it has claimed to have attacked.
Websites of Chinese news organisations said there had been public discussion of a "May Day war" in newsgroups in China. Many of the attacks that have occurred have been aimed at US Government organisations and six high-profile sites have been defaced, including the Department of Labor, Department of Health and Human Services, and the website of the US Surgeon General.
On some sites pictures of the dead Chinese pilot Wang Wei were used, and on others pro-China messages were left
'Denial of service' attacks
However, not all the attacks were well aimed. The White House Historical Society website was defaced which, despite its name, is not run by the US Government. Instead, it sells White House memorabilia.
Those hit by the attacks likened it to a vandal spraying graffiti on a shop window. Many of the sites were restored to normal working after a couple of hours. Others are yet to be restored.
Many of the attacks have been dismissed as the actions of "script kiddies" who use software programs widely available on the net, rather than their deep knowledge of net software, to exploit well-known vulnerabilities in software.
But the FBI and the National Infrastructure Protection Center warned those looking after websites to be on their guard. Alerts issued by the organisations said there had been a "significant" rise in attempts to scan and probe websites.
The agencies speculate that this could be by hackers looking to place programs that can be activated to help with so-called "denial of service" attacks that flood sites with bogus messages making them unreachable.