NEW : Users in China are already getting alerts , one ex - journalist said . Google wo n't say how it knows we are behind the hacking . Security chief says it does n't want to give away anything that could help the investigation . Google advises users who get the message to strengthen passwords and update software . The Google Watch warns users to change passwords and upgrade software .
NEW : Users in China are already getting alerts , one ex - journalist said . Google wo n't say how it knows we are behind the hacking . Security chief says it does n't want to give away anything that could help the investigation . The Google Watch warns users to change passwords and upgrade software .