What is a Brute Force Attack? A Guide for IT Security Professionals

Cyberattacks are evolving fast, but some hacking methods remain stubbornly effective. Brute force attacks are a prime example—simple, relentless, and surprisingly successful. Despite advancements in cybersecurity, attackers still exploit weak passwords and poor security practices to break into systems.

If you work in IT security, you’ve probably dealt with or at least worried about brute force attacks. This guide breaks them down—how they work, why they’re effective, real-world examples, and, most importantly, how to defend against them.

A brute force attack is a hacking method that relies on trial and error to guess login credentials, or other sensitive information. Attackers use automated tools to cycle through password combinations until they hit the right one.

At first glance, brute force attacks seem like an outdated or inefficient tactic, but they work—especially when people still use weak passwords like "123456" or "password."

Brute force attacks take advantage of computing power and automation. Here are some of the most common approaches:

• Automated Guessing: Hackers use software to input login attempts at high speeds until they succeed.
• Dictionary Attacks: A program runs through a preloaded list of commonly used passwords.
• Hybrid Approaches: Attackers combine dictionary methods with small tweaks, like replacing letters with numbers (e.g., "P@ssw0rd").
• Manual Attempts: Sometimes, hackers make educated guesses using personal details like birthdays, pet names, or favorite teams.

It’s a numbers game—the more attempts an attacker makes, the better their chances. If you start to see repeated failed logon attempts (Event ID 4625 in the Security Event Log on Windows), this could be an indicator of a brute force attack.

Brute force attacks aren’t all the same. Understanding their variations can help you prevent them:

1. Simple Brute Force Attack: The hacker manually guesses weak passwords. Think of "qwerty" or "letmein."
2. Dictionary Attack: The attacker runs through a list of common passwords, hoping for a match.
3. Hybrid Attack: Combines dictionary methods with small modifications, like swapping "O" for "0."
4. Reverse Brute Force Attack: Instead of guessing passwords, attackers start with a known password and test it against multiple usernames.‍
5. Credential Stuffing: If login details from one breach are leaked, hackers test them on other platforms (because people often reuse passwords).

Brute force attacks shouldn’t work anymore, but they do. Here’s why:

• Weak Passwords: People still use simple or easy-to-crack passwords.
• Computing Power: Attackers can launch millions of attempts per second using modern hardware.
• Readily Available Tools: Brute forcing software is easy to find online, even for amateurs.‍
• Password Reuse: Once hackers crack one account, they can try the same credentials elsewhere.

When successful, brute force attacks can have serious consequences:

• Data Theft: Sensitive company and customer information gets exposed.
• Financial Fraud: Stolen credentials can lead to unauthorized transactions or ransomware attacks.
• Malware Installation: Hackers use access points to plant malicious software.
• Identity Theft: Hackers can utilize stolen information to steal the victims’ identities.
• Reputation Damage: A single breach can shatter customer trust and brand credibility.

Dell Data Breach (2024):

In April 2024, private information for over 49 million of Dell’s customers from 2017-2024 was made available for purchase on the dark web. The attack was carried out by an attacker who brute forced Dell’s online portal to gain access to sensitive information.  They then carried out social engineering attacks, posing as a Dell partner, or reseller,  to verify the data.

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T-Mobile Data Breach (2021): 

In August 2021, T-Mobile US experienced a significant data breach affecting over 40 million former and prospective customers, including 7.8 million existing postpaid customers. The attacker, John Erin Binns, gained access through an unprotected GPRS gateway in Washington by performing a brute force attack on an SSH login. This breach exposed sensitive personal information, including names, birthdates, Social Security numbers, and driver's license details.  This resulted in a $31.4 million settlement.

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Alibaba (2016):

Over 20 million accounts were compromised on Alibaba e-commerce site TaoBao via credential stuffing and due to weak passwords.  This particular attack highlighted the need for MFA, as well as how password reuse can be easily leveraged by attackers to gain access to victims’ accounts.  The fallout of the technical report on this attack resulted in a dip of Alibaba’s US based stocks.

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Dunkin’ Donuts (2015): 

While Dunkin’ Donuts wasn’t itself the target of a brute forcing attack in 2015, they did little to prevent such attacks against over 20,000 of their customers. This resulted in a lawsuit brought on by the State of New York, resulting in a settlement of hundreds of thousands of dollars.

So, how do you stop brute force attacks before they happen? Here are the best strategies:

1. Strengthen Password Policies

Encourage complex, unique passwords. Best practices include:
✔ At least 12 characters with uppercase, lowercase, numbers, and symbols.
✔ Avoiding common passwords like "password123."
✔ Using passphrases (e.g., "I!Love#CyberSecurity21").
✔ Not reusing passwords across different accounts.

✔ Not saving passwords in your browser.

✔ Use a password manager to store complex passwords.

‍2. Enable Multi-Factor Authentication (MFA)

Even if a password gets cracked, MFA (like text message codes or biometrics) can stop unauthorized access.

3. Limit Login Attempts

Lock accounts after too many failed attempts to stop automated guessing.

‍4. Use CAPTCHA Verification

Requiring CAPTCHAs during login can block bots from brute force attacks.

‍5. Encrypt and Salt Passwords

Store passwords using hashing algorithms with encryption and salting to make them harder to crack.

6. Monitor & Block Suspicious IPs

Track repeated failed logins and block IPs showing suspicious behavior.

7. Educate Employees & Users

Many breaches happen because someone doesn’t know they’re at risk. Teach staff and users about strong passwords, phishing risks, and security best practices.

Attackers don’t always build their own tools—they use existing ones. Here are a few:

• John the Ripper: Open-source password-cracking tool.
• Aircrack-ng: Focuses on cracking Wi-Fi passwords.‍
• Hashcat: A popular password hash-cracking tool

Brute force attacks aren’t going away anytime soon, but neither are IT security professionals. The key is staying proactive—strengthen password security, educate users, and leverage modern defenses like MFA and encryption.

At the end of the day, cybersecurity is a constant battle between attackers and defenders. The more layers of security you put in place, the harder it becomes for hackers to break through.

Stay informed, stay vigilant, and keep your systems secure. Request a Huntress demo or start a free trial today.