Joanne Peters, a spokeswoman for the Department of Health and Human Services, said visitors to the Marketplace were unable to access the website because the contractor running the data hub experienced a "failure in the networking component that brought down network connectivity to the site," Politico reported.
The contractor -- Terremark, a subsidiary under Verizon-- provides information technology services including managed hosting, disaster recovery, security, data storage and cloud computing services.
Terremark "had a network failure that is impacting a number of their clients including HealthCare.gov," Peters said in a statement.
She said HHS Secretary Kathleen Sebelius spoke with the chief executive officer of Verizon Sunday afternoon "to discuss the situation and they committed to fixing the problem as soon as possible."
Terremark's failure is likely affecting other sites -- such as state-run exchanges -- besides HealthCare.gov and the federal data hub, Peters said.
The data hub of Terremark is crucial for determining private health insurance shoppers' eligibility for health coverage and federal subsidies and transmitting their personal information from various federal agencies to the exchange.