SolarWinds hack was work of 'at least 1,000 engineers', tech executives tell Senate

True scope of the breach, which affected 100 companies and several federal agencies, is still unknown

Tech executives revealed that a historic cybersecurity breach that affected about 100 US companies and nine federal agencies was larger and more sophisticated than previously known.

The revelations came during a hearing of the US Senate's select committee on intelligence on Tuesday on last year's hack of SolarWinds, a Texas-based software company. Using SolarWinds and Microsoft programs, hackers believed to be working for Russia were able to infiltrate the companies and government agencies. Servers run by Amazon were also used in the cyber-attack, but that company declined to send representatives to the hearing.