Poloniex has reset some of their user’s user’s passwords after a list of alleged username and password combinations was found circulating on Twitter. The trading platform is forcing a password reset on any email addresses that do not have an account with them. It is not known how this list of accounts was created, but it could have been compiled via credential stuffing attacks using accounts leaked in other data breaches. BleepingComputer suggests that all Pol on-site users reset their passwords to be safe.
Source: https://www.bleepingcomputer.com/news/security/poloniex-forces-password-reset-after-data-leak-found-online/