Reuters/Brendan McDermid Major firms like Microsoft and top government agencies were attacked, and sensitive data was exposed. Here's a simple explanation of what happened and why it's important. SolarWinds, a major US information technology firm, was the subject of a cyberattack that spread to its clients and went undetected for months, Reuters first reported in December. Foreign hackers, who some top US officials believe are from Russia, were able to use the hack to spy on private companies like the elite cybersecurity firm FireEye and the upper echelons of the US Government, including the Department of Homeland Security and Treasury Department.