Jim Chanos just pitched an Alibaba short and shares are falling

Jim Chanos presented at Morgan Stanley's secretive Miami conference, Lyford Cay, and his idea was to short Chinese internet retailer Alibaba.

He also recommended going long its competitor, JD.com.

He cited "accounting concerns" in his Alibaba thesis, according to CNBC's Scott Wapner. Shares of the company are now down 5% in today's session.

Alibaba, helmed by Chinese billionaire Jack Ma, went public on the New York Stock Exchange last year.

At the time Chanos said publicly, "quick little thought about Ali Baba: everyone forgets that he was a thief." Chanos reportedly also said that Alibaba's true margins may be "hard to know."

Alibaba today: