** Shares of cryptocurrency exchange Coinbase Global COIN.O fall 3% to $255.53 in premarket

** Co says it expects to incur between $180 million and $400 million in costs related to a cyber attack

** COIN says cyber criminals had stolen account data for a "small subset" of its customers

** However, COIN says no passwords, private keys, or funds were exposed and Coinbase Prime accounts are untouched

** The company will also not pay the $20 million ransom demand it received

** As of last close, COIN has gained nearly 6% YTD

(Reporting by Pritam Biswas in Bengaluru)

((Pritam.Biswas@thomsonreuters.com))