An anonymous reader quotes a report from Wired:

The U.S. Department of Justice, Mandiant, and Microsoft stumbled upon the SolarWinds breach six months earlier than previously reported, WIRED has learned, but were unaware of the significance of what they had found. The breach, publicly announced in December 2020, involved Russian hackers compromising the software maker SolarWinds and inserting a backdoor into software served to about 18,000 of its customers. That tainted software went on to infect at least nine US federal agencies, among them the Department of Justice (DOJ), the Department of Defense, Department of Homeland Security, and the Treasury Department, as well as top tech and security firms including Microsoft, Mandiant, Intel, Cisco, and Palo Alto Networks. The hackers had been in these various networks for between four and nine months before the campaign was exposed by Mandiant.

WIRED can now confirm that the operation was actually discovered by the DOJ six months earlier, in late May 2020 — but the scale and significance of the breach wasn’t immediately apparent. Suspicions were triggered when the department detected unusual traffic emanating from one of its servers that was running a trial version of the Orion software suite made by SolarWinds, according to sources familiar with the incident. The software, used by system administrators to manage and configure networks, was communicating externally with an unfamiliar system on the internet. The DOJ asked the security firm Mandiant to help determine whether the server had been hacked. It also engaged Microsoft, though it’s not clear why the software maker was also brought onto the investigation.

It’s not known what division of the DOJ experienced the breach, but representatives from the Justice Management Division and the US Trustee Program participated in discussions about the incident. The Trustee Program oversees the administration of bankruptcy cases and private trustees. The Management Division advises DOJ managers on budget and personnel management, ethics, procurement, and security. Investigators suspected the hackers had breached the DOJ server directly, possibly by exploiting a vulnerability in the Orion software. They reached out to SolarWinds to assist with the inquiry, but the company’s engineers were unable to find a vulnerability in their code. In July 2020, with the mystery still unresolved, communication between investigators and SolarWinds stopped. A month later, the DOJ purchased the Orion system, suggesting that the department was satisfied that there was no further threat posed by the Orion suite, the sources say.

According to WIRED, the DOJ said it “notified the US Cybersecurity and Infrastructure Agency (CISA) about the breach at the time it occurred — though a US National Security Agency spokesperson expressed frustration that the agency was not also notified.”

“But in December 2020, when the public learned that a number of federal agencies were compromised in the SolarWinds campaign — the DOJ among them — neither the DOJ nor CISA revealed to the public that the operation had unknowingly been found months earlier. The DOJ initially said its chief information officer had discovered the breach on December 24.”