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.  

Moreover, the analyst noted that the Bitcoin transfers in question were manual. An exchange transfer would be automatic. Hence, it is unlikely that a major institutional player was behind the enormous Bitcoin moves. 

The recent transfers are not what one would expect to see when an ordinary ancient whale decides to cash out. 

If Grogan's theory is correct, this could likely be the biggest cryptocurrency theft ever. However, it is worth reiterating that there is only a small probability that this was the case. Grogan has stressed that he is "speculating on straws" in this case.  

According to data provided by Arkham Intelligence, a single entity moved $8.6 billion worth of Bitcoin from a total of eight addresses. All these coins had remained untouched for a total of 14 years. 

The coins have so far not been moved from the new addresses, according to Arkham.