When web sites are hacked, hackers steal a treasure trove of information, which unfortunately sometimes includes usernames and passwords ("credentials"). This information is then often sold on the black market, or just released to the public, depending on whether the hacker is motivated by financial gain, fame, or simple mayhem. As soon as these stolen credentials are released, hackers worldwide immediately start trying to log in to many other web sites with the same or slightly-modified credentials - they use tools to do this with amazing efficiency. For this reason, if you re-use the same username and password for multiple web sites, it is only a matter of time until your accounts are hacked by one of these credential-stuffing attacks. One of the most-helpful resources to help you see whether a specific email address, phone number, or password has been involved in a data breach is to check the web site https://haveibeenpwned.com, which was developed by security expert Troy Hunt. Quite a few password manager tools integrate with this web site to make sure that your chosen passwords are not recognized as having been involved in a previous data breach (in which case, they will warn you). Password managers support you by suggesting secure passwords that avoid password reuse, and they encourage you to regularly change your passwords. In these ways, password managers lead you to practice good "digital hygiene."