Google has said it could cease its business operations in China, after Google email accounts belonging to Chinese human rights activists were hacked.

The American company said it started an investigation in December after discovering “a highly sophisticated and targeted attack”, originating in China, resulting in the theft of intellectual property.

Google said enquiries revealed a number of Chinese companies had also been targeted, including firms in the technology, chemical and media sectors.

The aim was to access Google email (Gmail) accounts of Chinese human rights activists, although investigators believe the hackers were largely unsuccessful and unable to read emails in the two accounts they did get access to.

Writing on Google’s official blog, corporate development and chief legal officer, David Drummond, said evidence of other attacks has also been found. He said the accounts of dozens of Gmail users across Europe and China appear to have been “routinely accessed by third parties”.

In light of these discoveries, Google has now threatened to pull out of China altogether. It is reviewing the feasibility of its business operations in the country and has decided it is no longer prepared to censor results on Google.cn. If negotiations with the Chinese government to run an uncensored search engine are unsuccessful, Google has said it will shut down the service and potentially close its China office.

Drummond said there are more issues to consider than simply security – the main one being freedom of speech.

He said: “We launched Google.cn in January 2006 in the belief that the benefits of increased access to information for people in China and a more open Internet outweighed our discomfort in agreeing to censor some results.

“At the time we made it clear that ‘we will carefully monitor conditions in China, including new laws and other restrictions on our services. If we determine that we are unable to achieve the objectives outlined we will not hesitate to reconsider our approach to China.’”