Sophisticated Chinese government hackers are believed to have compromised dozens of U.S. government agencies, defense contractors, financial institutions and other critical sectors, according to a private cybersecurity firm working with the federal government. The intrusions are ongoing, the FireEye security company said, and are the latest in a series of disturbing compromises of government agencies and private companies. The investigation is in its early stages but already has turned up evidence that the intruders breached sensitive defense companies, according to FireEye. That was not the case with the Russian SolarWinds campaign, which compromised nine federal agencies but not the Pentagon or its contractors, U.S. officials said.