The U.S. National Security Agency is built a system that would help identify cyber-attacks on critical U.S. infrastructure, as said by a source in the Wall Street Journal that cites unnamed sources.

The system would monitor both private U.S. companies and government agencies that manage infrastructure such as electricity grids and nuclear power plants, the story reports. It would use sensors positioned in PC networks that probable triggered by activity signaling a cyber-attack.

The U.S. government is more and more aware and suspicious of intrusions from overseas into public and private networks, mainly for the purpose of spying. A report commissioned by a congressional optional panel and launched last year found that China is possibly spying on U.S. companies and the government. The report found that at least 10 to 20 terabytes of sensitive data had been taken from U.S. government networks as part of a long-term campaign.