Every time a major data breach hits the news—whether it’s a social network, a retailer, or even a government database—millions of stolen usernames and passwords end up on the dark web. While many people shrug this off, cybercriminals see a golden opportunity: credential stuffing. This attack technique, which relies on the simple fact that people reuse the same passwords across multiple accounts, has become one of the most common ways hackers break into systems today.

Here’s how it works. Attackers take leaked credentials from one breach and automatically test them across dozens of other platforms using bots. If a user reused the same login for their email, bank, and shopping account, criminals can instantly gain access. In fact, studies show that over 60% of users reuse passwords across multiple sites, making credential stuffing incredibly effective.

The impact can be devastating. A single compromised email account can allow attackers to reset passwords for other services, intercept sensitive communications, or even impersonate the user for financial fraud. In 2023 alone, credential stuffing accounted for billions of login attempts worldwide, costing businesses an estimated $6 billion in fraud and remediation costs. For individuals, it often means drained bank accounts, hijacked social media profiles, or unauthorized purchases.

What makes credential stuffing so dangerous is its invisibility. Unlike brute-force attacks, which are noisy and obvious, credential stuffing looks like normal login activity—just at massive scale. Bots rotate IP addresses, mimic human behavior, and often succeed before security teams notice.

So, what’s the defense? The first line is unique, strong passwords for every account—something most users still struggle with. Password managers can help make this practical, generating and storing complex credentials without relying on memory. Multi-factor authentication (MFA) is also critical, as it can stop attackers even if they have the right password. On the enterprise side, businesses need tools like bot detection, login velocity checks, and adaptive authentication to flag suspicious login attempts.

The truth is simple: passwords alone are no longer enough. As long as people reuse them, credential stuffing will thrive. Breaking the cycle means changing user habits and pushing businesses to adopt stronger authentication practices. Otherwise, this quiet but powerful attack will remain one of cybercrime’s easiest wins.