Specifically, the Cybersecurity and Infrastructure Security Agency said it has determined that the SolarWinds Orion software vulnerability disclosed earlier this week is not the only way hackers compromised a variety of online networks - warning that in some cases, victims appeared to have been breached despite never using the problematic software.

The news will likely only compound already escalating concerns about the scale and scope of the data breach, which CISA said "poses a grave risk" to networks across both the public and private sector.

"CISA has determined that this threat poses a grave risk to the Federal Government and state, local, tribal, and territorial governments as well as critical infrastructure entities and other private sector organizations," the alert issued by the agency said. "CISA expects that removing this threat actor from compromised environments will be highly complex and challenging for organizations."