Swoben and the federal government aren’t the only ones dogging UnitedHealth. One of its former executives launched a similar suit in 2011 accusing the company of defrauding taxpayers. DOJ is now seeking to combine that suit with Swoben’s.

Investigations by journalists and government auditors in recent years have uncovered evidence of significant Medicare fraud by both insurers and providers.

The Center for Public Integrity reported on numerous instances of risk-score abuse by insurers in 2014 and alleged that insurers had “muzzled” investigation by Congress and regulators through influence-peddling.

Agencies have been aware of massive overpayments for years, the reporting argued, but they were reluctant to go public with their findings due to embarrassment and industry pressure.

In 2013, for instance, the Centers for Medicare and Medicaid Services estimated that 9.5 percent of the payments made to Medicare Advantage plans were improper. But the agency balked at implementing a proposed regulation in the following year to require insurers to report any improper payment they have received for a patient.

“The government isn’t in the best light when there’s that high an error rate,” health care attorney Thomas Hill said at the time. “They are reluctant to expose that to the world.”

In 2015, a federal audit that was published appeared to confirm the worst fears about Medicare Advantage. It concluded that the federal government had overpaid for half of all of the patients enrolled in UnitedHealth’s Medicare Advantage plan.