(CNN) US officials monitoring for cyber threats to the nation's critical infrastructure became aware several months ago of suspicious activity that's now been linked to one of the largest hacking operations in history, three sources familiar with the situation told CNN. Despite these initial indicators, the tremendous scope of the espionage campaign and its sophistication only became clear last week, after the elite cybersecurity firm FireEye disclosed a devastating data breach on its own network. The US government's early detection, which has not been previously reported, did not provide conclusive evidence that the government's networks had been compromised, but it was enough to worry top cybersecurity officials that potential vulnerabilities existed. The revelation illustrates how a select few within the government's most classified corners grappled with early warning signs of the massive hack -- and launched into a months-long investigation that ended up uncovering links to the devastatingly sophisticated spying operation that has rocked Washington this week. At least a half a dozen federal agencies are now known to have been targeted, including the Department of Homeland Security's cyber arm and the Departments of Agriculture, Commerce, Energy and State.

Source: CNN December 19, 2020 00:50 UTC