The nature of cyberwarfare in the People's Republic of China is difficult to assess. Government officials in India and the United States have traced various attacks on corporate and infrastructure computer systems in their countries to computers in the People's Republic of China. However, "It is nearly impossible to know whether or not an attack is government-sponsored because of the difficulty in tracking true identities in cyberspace." China has denied accusations of cyberwarfare, and has accused the United States of engaging in cyberwarfare against it, which the US government denies. A number of private computer security firms have stated that they have growing evidence of cyber-espionage efforts originating from China, including the "Comment Group".