The hack allowed them to access the personal data of 75,000 individuals, according to the Centers for Medicare and Medicaid Services (CMS), which revealed that the information was taken through a system that is typically used by insurance agents and brokers.
The CMS revealed that on October 13, it noticed "anomalous activity in the Federally Facilitated Exchanges, or FFE's Direct Enrollment pathway for agents and brokers".
As many as "75,000 individuals' files were accessed", the CMS confirmed, adding that it subsequently took measures to secure the system.
Meanwhile, the National Cyber Security Centre (NCSC) recently revealed that it has blocked Britain falling victim to almost 1,200 attacks over a two-year spell.
The organisation said it is currently beating around 10 attacks every week, and also revealed that the majority of the attacks were carried out by state-sponsored hackers.
Ciaran Martin, the head of the NCSC, explained: "We are calling out unacceptable behaviour by hostile states and giving our businesses the specific information they need to defend themselves."