Nothing to be concerned about. Its an opportunity if anything, just more great news! Bitcoin had a fork earlier in the year, meaning the data-log essentially split in to two ledgers, Bitcoin (BTC) and BitcoinCash (BTH). Coinbase is now implementing (BitcoinCash) so that the users that have had Bitcoin in their Coinbase wallets prior to the fork can now redeem the (BitcoinCash) that has been stored in the Coinbase servers ever since the fork of August 1st, 2017.