The company may be under criminal investigation for alleged irregularities in its Medicare business—but it's been touched by the Warren Buffett effect.

UnitedHealth Group ( UNH 12.04%) has been a solid dividend growth stock for years. Generally, its yield has been fairly low, due to the stock's rising value. Even as the healthcare insurance giant has grown its dividend, its yield hasn't been particularly high or noteworthy.

UNH stock soared after Warren Buffett’s Berkshire Hathaway revealed it bought shares of the healthcare company. Nonetheless, UnitedHealth faces a long list of unresolved issues.