UnitedHealth Group, the largest health insurer in the U.S., is under criminal investigation for alleged Medicare fraud, according to sources familiar with the matter. Federal prosecutors are reportedly scrutinizing whether the company manipulated billing data to improperly boost payments from the Medicare Advantage program. The investigation, which remains confidential, signals escalating government scrutiny over insurers' conduct within the multibillion-dollar Medicare Advantage system. If wrongdoing is found, it could lead to significant financial penalties and regulatory action against UnitedHealth. Neither the Department of Justice nor UnitedHealth has publicly commented on the investigation. However, the probe adds to mounting concerns about systemic overbilling and abuse in the Medicare Advantage sector — a program that now covers more than half of all Medicare beneficiaries in the United States.