How to Prevent Brute Force Attacks

A brute force attack is a method of trying to gain unauthorized access to an account or system by trying different credentials, through sheer trial-and-error, until one works. This is done by hackers running automated software or bots or using manual persistence of trying thousands of different username and password combinations. 

Even though it sounds pretty rudimentary compared to more advanced fraud tactics, it’s a very common way for fraudsters to hack into systems due to the frequency of weak and reused passwords. For any business with a login portal, understanding this attack, and where standard defenses of it fall short, is the first step toward actually stopping it.

What is a brute force attack?

A brute force attack is a hacking method where fraudsters test username and password combinations against an account login screen until managing to find a working pair. The simplest version of brute force attacks uses every single possible combination against one account, but in practice, it’s rarely performed in this manner since most systems will lock out a user after failing a few attempts in a row.

Instead, brute force attacks today fall into a few other variants:

• Credential stuffing takes username and password pairs already exposed in a prior data breach and tests them against other services, betting that a meaningful share of users reuse the same password across several accounts. 

• Password spraying flips the approach, testing one common password, such as a seasonal phrase and a year, against many different usernames, one attempt per account, which keeps the attack under most lockout thresholds. 

• Reverse brute force starts from a known password and searches for the username it belongs to, useful when a fraudster has a leaked password but not the associated account.

How fraud teams can prevent brute force attacks

The Cybersecurity and Infrastructure Security Agency (CISA) has published guidance on this pattern for years, and the core mitigations have stayed consistent even as attack tooling has gotten faster.

Rate limiting and account lockout thresholds slow down traditional brute force attempts against a single account, though they do little against password spraying, which spreads attempts across many usernames to stay under any one account’s threshold.

Multi-factor authentication (MFA) remains an important layer, but fraud teams should not treat it as sufficient on its own. Recent industry threat research has found that a large share of compromised accounts still had MFA enabled at the time of the breach, often because fraudsters paired credential attacks with MFA “push bombing,” repeatedly sending approval prompts until a user approves one out of frustration or confusion. CISA’s own advisory on Iranian state-linked cyber actors targeting critical infrastructure organizations documented this exact combination: brute force and password spraying paired with MFA push bombing to compromise accounts across healthcare, government, and energy sector organizations.

Behavioral and device signals catch what static thresholds miss. Sudden spikes in failed logins from a single IP address or device, login attempts using unusual user agent strings that do not match typical browser activity, and access attempts against accounts that have been dormant for months are all signals that layered detection can flag well before a successful login occurs.

Passwordless authentication, including passkeys and biometric login, removes the underlying vulnerability entirely, since there is no password for a fraudster to guess, stuff, or spray in the first place. Adoption is still growing across consumer and enterprise platforms, but it represents the most durable long-term fix available.

Why brute force attacks are still effective in 2026

The persistence of this attack pattern comes down to a straightforward mismatch. The average user’s password protection level hasn’t kept pace with the computing power available to fraudsters. Modern hardware can test an enormous amount of password combinations per second against weak passwords, and automated tooling makes running a credential stuffing or spraying campaign inexpensive on a large scale.

Because password reuse across many accounts is so common, a single breach at one unrelated company makes it much easier for fraudsters to gain entry in many different accounts at once. CISA has specifically called out federated single sign-on (SSO) and web-based applications as common targets for password spraying, since a single compromised set of credentials there can open access across an entire suite of connected services.

Detection is also harder than it looks. Because password spraying deliberately paces its attempts to avoid triggering lockouts, and credential stuffing uses credentials that are technically valid rather than guessed, many of these attacks look like ordinary login activity to systems that only monitor for obvious anomalies, such as a flood of attempts against one account.

Signals that indicate a brute force attack in progress

A few patterns consistently show up in brute force and credential stuffing campaigns, and fraud teams should build monitoring around them rather than waiting for an account lockout to trigger.

An unusual volume of failed login attempts across many different accounts, rather than concentrated on one, often indicates password spraying rather than a single user forgetting their password.

Login attempts originating from data center IP ranges, known proxy or VPN exit nodes, or a small number of IP addresses attempting logins against a large number of distinct accounts are classic signs of automated credential attacks rather than legitimate user behavior.

A spike in successful logins followed shortly by changes to account details suggests an attack has succeeded and the attacker is establishing persistence or preparing to monetize their access.

Repeated MFA approval prompts sent to a single user in a short window outside of normal work hours are a strong indicator of push bombing rather than an ordinary authentication hiccup. Fraud and security teams that treat a cluster of MFA denials or ignored prompts as noise risk missing the exact moment an attack is escalating from credential guessing to active account compromise.

If your fraud team has spotted signs of brute force attacks but isn’t sure how to stop them, Sift may be a great option. Sift analyzes behavioral and device signals in real time to flag credential stuffing and password spraying attempts before they turn into account takeover. Visit our solutions page to see how it works.

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