Скорее не на сервера, а в конкретный аккаунт
У слака в репорте вот такое есть:
2015
In 2015, unauthorized individuals gained access to some Slack infrastructure, including a database that stored user profile information including usernames and irreversibly encrypted, or “hashed,” passwords. The attackers also inserted code that allowed them to capture plaintext passwords as they were entered by users at the time.