How one stolen login travels
A password leak rarely stays confined to the service that was breached. Attackers may collect exposed username-and-password pairs and feed them into automated tools that test the same combinations on other sites. This is called credential stuffing: instead of guessing passwords, the script tries credentials that worked somewhere before.
The method exploits a common habit. People often choose a familiar password across multiple accounts, sometimes changing only a small detail. If a reused password opens an email account, for example, an attacker may also try it on shopping, banking, or social platforms associated with the same email address. A successful login can expose private information or give the intruder a foothold for resetting other passwords.
Why automation changes the risk
A person could not efficiently test the same login across thousands of services. Scripts can make those attempts quickly and repeatedly, while attackers may spread them across many accounts and websites. Even when most tries fail, a few reused passwords can be enough to make the effort worthwhile.
Websites use defenses such as limiting repeated login attempts and asking for an additional verification step. Those measures can slow or block an attack, but they do not make a reused password safe: a login may still succeed where protections are weaker, or where an attacker can access a session another way.
Break the chain between accounts
A password manager helps by generating and storing a different, hard-to-guess password for each service. Then a password exposed in one breach does not automatically unlock another account. Unique passwords turn one leaked key into one compromised door, rather than a key that may fit across your digital life.
