It's tough to trace hackers, says internet security expert

As the Hong Kong government asks the US to clarify Edward Snowden's claims of hacking in the city, an internet security expert says it's tough to trace when hackers attack, where they operate from and what information they steal.

"Logins would be completely erased by hackers after they get what they want," said Matthew Wong Yun-lam, a security consultant for US-based internet security firm FireEye.

If the Hong Kong government was using a US-developed computer operating system, such as Microsoft Windows, a US hacker would likely know how to break into it in the most discreet way.

"If the product is developed and hacked by the same bunch of people, they know where the back doors of the system are and know exactly how to overwrite the logins," said Wong. "Basically, you just can't follow up on the hack."

Among Snowden's claims was that leading US IT firms shared information, including vulnerabilities in their products, with the government.

As well as public officials, Snowden said the US launched hacking attacks on business targets in Hong Kong. Wong said over 90 per cent of his clients locally had computers compromised without their knowledge.