Brute force attacks: How they work & how to prevent them

Compromising login credentials is the goal of many modern cyber-attacks. According to Verizon’s 2025 Data Breach Investigations Report, 88% of web application attacks over the past year involved the use of stolen credentials, demonstrating how vulnerable password-based systems remain without proper security controls.

Among the many techniques hackers use for credential-based attacks, one of the oldest and most common methods for guessing a user’s password is the brute force attack. Despite their simplicity, these attacks can be highly effective, especially when users rely on weak or commonly used passwords.

In this article, we’ll cover what brute force attacks are, how they work, and how organizations can defend against them.

What are brute force attacks?

Brute force attacks are relatively straightforward to understand. They’re essentially an unsophisticated yet highly effective method of decoding encrypted data such as passwords. Cybercriminals use tools to test all possible password combinations through countless login attempts until the correct one is identified. The more computing power they have, the faster this process becomes – especially if weak passwords are involved.

However, not all brute force attacks are the same. Cybercriminals employ a range of tactics from simple attacks, which test every possible password combination, to more nuanced approaches such as the hybrid attack and reverse attack. Each method has a distinct strategy behind it, but the motives behind brute force attacks are the same – cracking passwords to gain unauthorized access to protected information.

Types of brute force attacks

The nuances between these types of attack highlight the evolving sophistication of cybercriminals and underscore the need for staying on top of your defensive measures.

• Simple brute force attacks: Attackers use a systematic trial-and-error method to guess password combinations. This type of attack is exhaustive and can be time-consuming, but it’s effective if the target has weak cybersecurity measures in place.
• Dictionary attacks: Involves attempting all the words in a pre-defined list or “dictionary” of common passwords. Dictionary attacks exploit users’ tendencies to use simple, easily remembered (and easily guessed) passwords. They can be highly effective against organizations who have failed to implement strong password policies.
• Reverse attacks: Instead of trying many passwords for one user, the attacker tries a common password with many different usernames within an organization. This type of attack capitalizes on users often going for the same weak passwords, meaning it’s likely to have been chosen by at least one person.
• Hybrid attacks: Combines elements of both dictionary and simple brute force attacks, using a dictionary of passwords but with added numerical or special character combinations.

Real-world example of a brute force attack

• Date: August 2021
• Target: T-Mobile
• Attack method: Brute force attack led to unauthorized access
• Impact: Over 37 million users’ data exposed, including SSNs and ID info

In August 2021, T-Mobile, one of the largest wireless network operators in the US, fell victim to a substantial cybersecurity breach traced back to a brute force attack. The incident led to the exposure of sensitive personal data of over 37 million past, present, and prospective customers. The stolen data included social security numbers, driver’s license information, and other personally identifiable data.

This incident highlighted the vulnerability of even major organizations to brute force attacks and reinforced the need for robust cybersecurity measures. Even though passwords are encrypted and stored as password hashes, attackers can still “guess” the passwords until they successfully match the password represented by the password hash.

How to detect brute force attacks

Detecting an attack early is critical to preventing unauthorized access. These attacks often follow identifiable patterns that security teams can monitor using proper alerting and anomaly detection tools. Here are the key indicators and techniques for detecting brute force attacks:

1. Unusual number of failed login attempts

A sudden spike in login failures — especially from a single IP address — is one of the most common signs of a brute force attack in progress. Look out for:

• Dozens or hundreds of failed attempts in a short period
• Repeated attempts on the same account
• Sequential attempts across multiple accounts

2. Logins from unusual locations

Brute force tools often run on remote machines or botnets in foreign countries. If you notice login attempts from IP addresses or regions not normally associated with your organization, it could be a sign of malicious activity.

3. Repeated login attempts with common usernames

Attackers frequently target default or common usernames (like admin, test, or user1). Seeing repeated login attempts for these accounts, especially with simple or default passwords, may signal a reverse brute force attack.

4. High authentication traffic outside of normal business hours

Most brute force attempts are automated and run continuously, even during nights and weekends. That means any spikes in login traffic during off-peak hours should trigger alerts and warrant further investigation.

5. Repeated account lockouts

Frequent lockouts for specific users can signal an attacker trying to guess credentials. If multiple users across departments are being locked out without attempting to log in, investigate immediately.

How to prevent brute force attacks

There are several preventative cybersecurity measures that organizations should be using in collaboration to lower the risk of being caught out by a brute force attack.

Longer, stronger passwords

By increasing password length and incorporating a mix of uppercase and lowercase letters, numbers, and special characters, the number of possible passwords skyrockets, making brute force attacks exponentially more challenging – even with large amounts of computing power. The best way create a long password over 20 characters is through a passphrase where three random memorable words are strung together with a few lesser used special characters incorporated.

Unsure how many people in your organization are using weak or compromised passwords? Run a free audit today with Specops Password Auditor for a full picture of your password risks.  

Multi-factor authentication

Implementing multi-factor authentication (MFA) is another effective strategy for combating brute force attacks. By requiring users to verify their identity through a secondary method, such as a mobile app or a text message code, MFA dramatically reduces the likelihood of unauthorized access, even if a password is compromised.

Monitor for unsuccessful login attempts

Monitoring for multiple unsuccessful login attempts can also serve as an early warning sign of an attack in progress. Many systems implement account lockout or delay policies after a certain number of failed login attempts, preventing further attempts, and effectively thwarting simple attacks.

Secure your systems against brute force attacks with Specops Password Policy

While these measures can significantly bolster defenses against attacks, managing them can be a daunting task for IT Security teams. Specops Password Policy enhances security by preventing users from choosing common password patterns and continuously scanning for known breached passwords, making it exponentially harder for an attack to be successful. The Breached Password Protection feature references a list of over 4 billion compromised passwords, even those being used in attacks right now.

Specops Password Policy also comes with a helpful end user interface to guide employees on creating longer, stronger passphrases that meet your organization’s password policy requirements. Try Specops Password Policy for free today and secure your users against password attacks.

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