Shares of UnitedHealth Group surged nearly 14% on Friday after billionaire Warren Buffett's Berkshire Hathaway bought 5 million shares of the company, providing a shot in the arm for investors who think the health conglomerate will turn around under its new CEO.

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

Unsurprisingly, the options pits are seeing ample activity. So far 377,000 calls and 121,000 puts have been exchanged so far, 6 times the average daily pace. Most popular are the expiring August 300, 305, and 310 calls, where new positions are being opened.