Getting hacked these days is more a question of “when” rather than “if” these days. These details are then commonly shared or sold on various Dark Web forums. Microsoft’s “hacked” app will detect if any of your email addresses are detected in these databases and let you know immediately.
The app uses the industry-trusted Troy Hunt’s massive haveibeenpwned database of breaches.
Armed with this information, you can change your password(s) immediately before further damage gets done.