"Our internal IT security team recently identified an apparent external cyber-attack on USIS’ corporate network. We immediately informed federal law enforcement, the Office of Personnel Management (OPM) and other relevant federal agencies," they stated.
"We are working closely with federal law enforcement authorities and have retained an independent computer forensics investigations firm to determine the precise nature and extent of any unlawful entry into our network. Experts who have reviewed the facts gathered to-date believe it has all the markings of a state-sponsored attack."
No more details have been shared as the investigation is still ongoing, but according to the Washington Post, the US Department of Homeland Security and the US Office of Personnel Management have temporarily suspended work with the company. Given that some of the DHS employees might have been affected, all received a notification about it.
The company has also welcomed an US-CERT team, and they are conducting an on-site assessment and advising the company in regards to breach mitigation.
Unofficial sources say that this intrusion is seemingly not related to a breach of the Office of Personnel Management's networks discovered earlier this year and traced back to China.