ISEC said it discovered the additional targets while working with victims of the attack, which originated in China. Google initially alerted 30 companies to the problem, San Francisco-based ISEC said.

Google disclosed last month that it suffered highly sophisticated—cyber attack on its corporate infrastructure and threatened to withdraw from China. The Mountain View, California-based company said Gmai] e-mail accounts of Chinese human-rights activists were targeted by the hackers.

Chief Executive Officer Erie Schmidt said Jan. 21 that Google had begun talks with the Chinese government and would be—making some changes—to its operations in China. The company was still following Chinese laws and censoring its search results locally, he said.

Although none of the attacks or technique used in this series of attacks are particularly novel, the skill set, patience and tenacity of the attackers is much greater than most enterprises are equipped to deal with,” ISEC said in its report.

Jill Hazelbaker, a Google spokeswoman, didn’t immediately respond to a message seeking comment,

An exit from China would cost Google $600 million in annual sales, with would be advertising clients instead spending at rival Baidu Inc.. JPMorgan Chase & Co. said in January. As concerns ease the Chinese government will shut the company’s operations, advertisers are returning and Google’s China business is hiring again, media buyers said earlier this month.

China, whose authorities censor media through state ownership of all newspapers, television and radio stations, may have 840 million Internet users, or 61 percent of the population, by 2013, according to EMarketer Inc. in New York. The country had 384 million users at the end of last year, according to government data.