How it works
Billions of leaked credentials circulate on criminal forums, collected from past breaches and from infostealer malware. Attackers load them into tools that try each pair against login pages for email, VPNs, SaaS applications and online shops, spreading the attempts across many IP addresses to avoid detection.
Credential stuffing vs brute force
A brute force attack guesses passwords. Credential stuffing uses real passwords that already worked somewhere else, so its success rate is much higher and each attempt looks like a normal login.
How to protect against it
MFA is the most effective measure, because a correct password is no longer enough. A password manager removes password reuse, and SSO reduces the number of separate logins. On the service side, rate limiting, bot detection and checking new passwords against lists of known leaks help. Anyone can check whether their email appears in known leaks on Have I Been Pwned.
Why it matters for companies
A single reused password on a work account can open email, file storage or a VPN, and lead to BEC fraud or ransomware. Monitoring logins and blocking suspicious sign ins closes the gap.
