Sources told press agency Reuters that the Chinese hackers may have had help from one or more employees at Google's office in China.
The sources, who are familiar with the situation, told Reuters that the attack, which targeted people who have access to specific parts of Google networks, may have been facilitated by people working in Google China's office.
"We're not commenting on rumour and speculation. This is an ongoing investigation, and we simply cannot comment on the details," a Google spokeswoman said.
Security analysts told Reuters the malicious software (malware) used in the Google attack was a modification of a trojan called Hydraq. A trojan is malware that, once inside a computer, allows someone unauthorised access. The sophistication in the attack was in knowing whom to attack, not the malware itself, the analysts said.