The online sparring match between supposed US and Chinese hacking groups appears to have stepped up, with widespread media reports of the possibility of increased attacks starting today, International Workers Day.

However, security experts have pointed out the dangers in assuming that US hackers are attacking China and vice versa. It could be anyone doing the defacing and laying the blame on someone else, they warned.

Rumours circulating on the web claim that Chinese hackers will be kicking off a 'Hack the USA' week today, while numerous Chinese Government sites have been defaced in what could be seen as retaliation.

Almost 40 Chinese and US sites have been attacked in the last 24 hours, with the numbers surging into the hundreds over the last month.

US sites for the departments of Labour and Health and Human Services were compromised recently, with the index pages replaced with a picture of Wang Wei, the Chinese pilot killed in the spy plane collision.

Chinese Government sites have also been defaced with messages calling for "American hackers ... join our work and hack together Chinese sites".

But as Sarah Gordon, senior research fellow for security firm Symantec, pointed out: "There is no proof that these hacks are being carried out by US or Chinese hackers. The virtual world allows for so much anonymity. Add this to the dangerous ways that some computers can be used, such as for propaganda purposes, and the internet is an ideal tool for cybercrime and terrorism."

In fact, Poizonb0x, a defacing group claiming the credit for over 200 Chinese domains defaced last month, said in an interview with Brass Knuckles webzine that the attacks were not politically motivated.

"We could crack all *.au sites too ... no politics! No plans! ... I'm not an American," said a Poizonb0x spokesperson.

But the unverifiable motive for the attacks has not stopped risk management firms like iDefense releasing reports suggesting the attacks on US sites are "state-sponsored" by China.

One spokesman for iDefense is quoted as saying: "But the Chinese Government tries to control the internet closely and attempts to filter Western influences, so it leads to the suspicion they're at least looking the other way."