Coinbase lost control over ETC tokens.

Charlie Lee from Coinbase said on tweeter:  

"yes, we made a conscious decision to not protect the ETC [blockchain]".

This decision allowed hackers to steal customer's ETC tokens from their users.

ETC stands for Ethereum Classic which is the original Ethereum blockchain.

Ethereum blockchain was recently hard forked by the Ethereum Foundation in order to recover funds lost in foundation's greatest disaster - The Dao. The Dao is, or rather was, a Decentralized Autonomous Organization (DAO) governed by laws written in computer program. Unfortunately the code used wasn't properly tested and allowed hackers to steal (transfer away) funds from investors.

The hard fork performed by the Ethereum Foundation was highly controversial due to violation of its catchy term of service statement : "the code is law".