J.P. Morgan Chase said the incidents were sporadic, limited, and due to an internal glitch.
We suggest customers log in to their Chase accounts to check activity and report anything suspicious. Also, it's a good idea to reset you password. Doing both of these activities will give you a reference point for your account's activity, and the active credentials to the account.
Krebs reports more details on the story, here:
https://krebsonsecurity.com/2018/02/chase-glitch-exposed-customer-accounts/