FireEye's CEO also said it's difficult to know whether a mysterious postcard was in fact sent by a Russian intelligence agency.

Its intelligence services will remain a standalone company under the Mandiant name, pending approval.

The U.S. government has also been affected.

The new SolarWinds timeline places the earliest activity at around eight months earlier than previously disclosed.

A national breach notification law needs to be simple and limited, officials said, but stopped short of endorsing a specific proposal.

The malware in questions bear similarities to another hacking tool named after the popular cartoon.