And you're going to take calculated risks as an attacker," one source familiar with the investigation said. FireEye has declined to provide additional details about how the hackers were ultimately discovered after evading detection for months, citing an ongoing investigation into the matter. US officials and experts warn the hackers used multiple entry points to breach these networks, some of which have not yet been identified. The fact that FireEye -- not the federal government -- discovered the breach has also raised questions about why the attack went undetected at US government agencies. While a private company spotted the breach, a private sector contractor, SolarWinds, was at least one of the entry points hackers used to break into government networks.

Source: CNN December 23, 2020 16:07 UTC