Authentication attacks are repeated attempts to test, reuse, or guess login details until a system accepts one. They include brute-force guessing, password spraying, and credential stuffing, where stolen usernames and passwords are tried across services. The goal is to get past the login screen without using a software exploit.
These attacks matter because valid credentials often look normal to security tools, especially when an attacker uses low-and-slow probing or signs in from familiar infrastructure. Defenders look for unusual login frequency, repeated failures, impossible travel, and logins to accounts that should not be active. Strong passwords, multi-factor authentication, rate limiting, account lockouts, and centralized alerting all reduce the chance that repeated login attempts become a working foothold.