Conor Grogan, director at Coinbase, believes that there is “a small possibility” that billions of dollars worth of long-dormant Bitcoins were moved earlier today as the result of a private key hack. 

Before the massive moves, one of the associated wallets made a small transaction on Bitcoin Cash. 

Grogan suggested that this could be a way of testing if the private keys that were used to control both BTC and BCH wallets actually worked. In such a way, it was possible for the hacker to avoid unwanted attention since very few people actively monitor the aforementioned blockchain. Other BCH wallets remained untouched, which seems to be odd.