Most hacks involve stealing user names and passwords, but this was far more sophisticated. Once they were in the SolarWinds network management software, the Russians, investigators said, were able to insert counterfeit “tokens,” essentially electronic indicators that provide an assurance to Microsoft, Google or other providers about the identity of the computer system its email systems are talking to. By using a flaw that is extraordinarily difficult to detect, the hackers were able to trick the system and gain access, undetected.
It is unclear exactly what they extracted; the situation is reminiscent of the Chinese hack of the Office of Personnel Management, which went on for a year in 2014 and 2015, with the loss eventually tallied at more than 22 million security-clearance files and more than five million fingerprints.