The Justice Department is looking into claims that four health insurers defrauded Medicare by claiming that patients were treated for illnesses they either never had or were never treated for, Reuters reports.

Health Net (HNT) , Aetna (AET) , Cigna's (CI) - Get Cigna Corporation Report Bravo Health and Humana (HUM) - Get Humana Inc. (HUM) Report are the four insurers that the DOJ is looking into, after the accusations were brought in a lawsuit.

A former United Health executive brought a False Claims Act lawsuit, Reuters noted, his whistleblower case against the insurers was filed under seal in 2011. The Justice Department filed a "corrected notice" on Tuesday saying that as a result of the ongoing investigations it could not make a decision about proceeding against the companies.

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