Brute Force Attacks Explained: How Password Cracking Works and How to Stay Safe

Brute Force is one of the simplest methods for password cracking: a program automatically checks numerous options until it finds the correct one. This approach is called a brute-force attack because it doesn't require exploiting complex vulnerabilities-just the ability to repeatedly test different combinations. In practice, the effectiveness of such an attack depends greatly on where it is performed. Attempts to log into an account through a standard login form can be limited by the server, while if a hash database is leaked, checking options can happen locally and at much higher speed. That's why modern security systems aim not only to make passwords harder to guess, but also to make mass verification of combinations either too slow or pointless.

What Is Brute Force and Why Is It Called Password Cracking?

A Brute Force attack is a method where the correct data is sought via systematically checking a large number of possible options. For passwords, the program generates a combination, tests it, and if unsuccessful, moves on to the next.

The main advantage for an attacker is simplicity. The algorithm doesn't need to know the password's structure or use a system vulnerability. If there's a finite number of possibilities and enough time to try them, the correct combination will eventually be found-at least in theory.

However, the word "theoretically" is key here. The number of possible passwords grows so quickly that a full brute-force attempt becomes virtually impossible, even with powerful hardware.

How Full Brute Force Works

Imagine a four-digit password. Each position can be a digit from 0 to 9, making 10,000 combinations-ranging from 0000 to 9999. A computer can sequentially check all of them.

If the password is extended to eight digits, the number of options rises to 100 million. If you add letters of both cases and special characters, the possible combinations skyrocket.

This is why password length is crucial. Adding each new character doesn't just increase the number of options-it multiplies it by the size of the character set.

For example, if there are 62 possible characters (uppercase and lowercase Latin letters plus digits) for each position, an 8-character password already has over 218 trillion possible combinations.

The speed of checking depends on the situation. Through a website login form, you can't send millions of requests per second: the server can introduce delays, block addresses, or limit attempts. If the attacker has data for local checking, web server restrictions don't apply.

Brute Force, Dictionary Attacks, and Guessing Popular Passwords

Full brute force checks all possible combinations, but starting with it isn't always rational. People seldom choose completely random passwords, so real-world attacks often begin by trying more likely options first.

A dictionary attack checks a precompiled list of words and passwords. This list might include common combinations like "password," "qwerty," number sequences, and other frequently used options.

Attackers may also test modified versions of ordinary words: letter-to-number substitutions, adding a year, a symbol at the end, or changing case. A password that appears more complex because of a single uppercase letter and an exclamation mark may still fit a common pattern.

Thus, Brute Force in a broader sense often includes not only literal full enumeration, but also more optimized guessing: starting with the most likely options, and only gradually expanding the search space if necessary.

How a Brute Force Attack Happens in Practice

Password cracking can occur in two fundamentally different ways: via the service itself or locally after obtaining a database of hashes. This directly affects the attack speed and the effectiveness of security measures.

In the first case, each combination must be sent to the server and wait for a response. In the second, the server isn't involved, and limits on the number of attempts no longer apply.

Online Brute Force via Login Forms

An online brute-force attack takes place directly through the login page of a website, application, or other service. For each attempt, the system receives a login and a guessed password, compares them to stored data, and returns a result.

This method has a serious limitation: the server controls the speed of verification. Even if a computer can generate huge numbers of passwords, it can't send them all at once.

A service might allow only a few attempts over a certain period, add delays after several wrong passwords, or temporarily block further logins. As a result, brute-forcing millions of combinations could take years.

Modern systems also analyze the source of requests. If the same IP address or account gets a constant stream of wrong passwords, this activity stands out from typical user behavior.

Therefore, classic brute-force attacks via login forms are rarely effective against well-configured services. The main risk arises for systems with no attempt limits or very weak user passwords.

Offline Cracking of Password Hashes

The situation changes after a database leak. Secure services should never store user passwords in plain text. Instead, they store the result of a special transformation-a hash.

When a user enters a password, the system computes its hash and compares it to the stored value. If they match, the password is correct.

After a database leak, the attacker doesn't need to interact with the site for each attempt. They can compute hashes of guessed passwords locally and compare them to the stolen value.

Here, there are no login form restrictions, server delays, or blocks after failed attempts. The speed depends mainly on the hashing algorithm and the hardware's performance.

That's why secure password storage is just as important as protecting the login page itself. Modern systems use special algorithms designed to make each password check require significant computing resources.

To learn more about why websites store hashes and the mechanisms protecting them after a leak, check out our article on Password Hashing: How Websites Secure User Credentials.

Yet, hashing doesn't make brute force impossible. If a user picks a short or common password, it can still be found among the first options checked. Therefore, protection operates on multiple levels: a strong password from the user, secure storage on the service side, and limits on login attempts.

What Determines Brute Force Speed?

The speed of a brute-force attack isn't determined by a single factor. It depends on password length, the size of the allowed character set, how passwords are stored, and whether the checking happens on the server or locally.

The same computer can check a huge number of options in one scenario and almost nothing in another. The bigger the space of possible combinations and the more resource-intensive each check, the harder the attack becomes.

Password Length and Number of Combinations

The key factor is password length. If each position can use N different characters and the length is L, the number of possible combinations is N^L.

For example, a password of only decimal digits has 10 options per position. A four-digit code offers 10,000 combinations, six digits-1 million, eight digits-100 million.

When letters and numbers are allowed, the search space grows even faster. With 62 possible characters, there are over 218 trillion combinations for eight positions.

Thus, increasing password length is usually more effective than just adding a special character. A password of 14-16 unpredictable characters creates far more brute-force options than a short combination that technically includes upper/lowercase, digits, and symbols.

Alphabets, Digits, and Special Characters

Expanding the set of allowed characters also increases the number of combinations. If a password uses only lowercase Latin letters, each position can be one of 26 characters. Adding uppercase letters doubles it to 52; with digits, it's 62.

Special characters further expand the search space, but don't guarantee security by themselves. A combination like a common word plus "1!" at the end might seem complex to humans, but remains predictable for automated guessing.

Brute-force programs consider common patterns: a to @, o to 0, appending the current year, a capital first letter, or an exclamation mark at the end. So, unpredictability is as important as formal complexity.

Why Hashing Slows Down Brute Force

In offline attacks, speed depends on how quickly each guessed password can be checked. If the hashing algorithm is very fast, hardware can try vastly more options in the same time.

That's why password storage relies on special algorithms designed for deliberately slow computation. Their goal is to make each check sufficiently costly in time and resources, drastically slowing mass brute force.

Additionally, a salt-a random value added to the password before hashing-is used. Thanks to salting, identical passwords for different users don't necessarily produce the same stored values.

Salt doesn't make the password itself more complex, but it prevents attackers from using precomputed hash tables against many accounts at once.

Thus, resistance to brute force depends on two components: the user chooses a long, unpredictable password, and the system makes each check computationally expensive. The stronger both layers, the less practical brute force becomes.

Why Modern Systems Are Protected from Brute Force

Modern brute-force protection isn't built on a single mechanism. Even if a user chooses a weak password, the service can make automated guessing much harder via speed limits, additional checks, and two-factor authentication.

The main goal is to deprive brute force of its core advantage: the ability to quickly try huge numbers of options.

Limiting Attempts and Adding Delays

The most obvious way to protect against brute force is to limit login attempts. If, after several incorrect passwords, a service introduces a pause, brute-force speed drops sharply.

For example, if checks are instant, a program could theoretically submit thousands of attempts in a row. If, after a few errors, the next attempt is only allowed after several seconds or minutes, even a modest combination set becomes extremely tedious to brute-force.

Some services gradually increase the delay. After the first few mistakes, the user barely notices, but if suspicious activity continues, the pauses get longer.

Another option is temporary blocking of accounts, IP addresses, or specific request sources. However, hard blocking is used cautiously: otherwise, an attacker could intentionally enter wrong passwords to lock out someone else's account.

That's why modern systems often combine several factors: number of attempts, request frequency, IP address, device characteristics, and login history.

CAPTCHA and Behavioral Analysis

If a system detects an unusually high number of login attempts, it may require extra confirmation that a human is logging in.

This includes CAPTCHA and other checks that disrupt fully automated brute force. The attacker must pass extra verification or find ways to bypass it, increasing the attack's cost.

More advanced systems may not display a visible CAPTCHA at all. Instead, the service analyzes behavior: frequency of requests, page navigation, browser parameters, device type, and more.

A typical user makes a few password mistakes, then either logs in successfully or initiates account recovery. Automated programs may send hundreds of identical requests, making their behavior stand out.

Two-Factor Authentication

Even successfully guessing the password doesn't guarantee account access. If two-factor authentication is enabled, a second confirmation is required after entering the correct password.

This could be a one-time code from an authenticator app, a physical security key, or a prompt on a trusted device.

In this case, the password is only the first layer of defense. Even if it's guessed or leaked, it's no longer enough for access.

For more on different types of two-factor authentication and their reliability, see our article Why Two-Factor Authentication Matters: Protecting Your Digital Life.

It's the combination of attempt limits, behavioral analysis, and additional authentication that makes classic online brute force far less effective. Instead of simply trying millions of combinations, an attacker faces several independent layers of defense.

How to Protect Yourself from Password Cracking

For everyday users, protecting against brute force means making your password an unattractive target and minimizing the consequences if it's ever compromised. Length, uniqueness, and unpredictability matter far more than simply including special characters.

Use Long, Unique Passwords

The longer the password, the more combinations must be checked in a brute-force attack. Thus, a long random combination or passphrase is usually more resilient than a short password, even if the latter includes digits, uppercase letters, and symbols.

It's equally important to use different passwords for different services. If the same password is used on multiple sites, a leak from one can put other accounts at risk-without any brute force required.

You don't have to memorize dozens of complex combinations. Password managers exist to generate random passwords and store them securely.

Enable Two-Factor Authentication

Two-factor authentication adds another layer of protection after the password. Even if an attacker obtains the correct combination, they'll still need to pass an additional step.

This is especially important for email, social networks, cloud services, and other accounts that can access personal data or reset passwords for other services.

If you have a choice, it's better to use an authenticator app, a hardware security key, or a trusted device. SMS codes also add a barrier but have their own limitations and risks.

Why Passkeys Virtually Eliminate Brute-Force Risks

Another approach is to do away with passwords altogether. That's the idea behind Passkeys, which use a cryptographic key pair instead of a secret you have to remember and enter.

When creating a Passkey, your device generates a private key (kept on your device) and a public key (sent to the service). During login, the server sends a request, and your device confirms it with the private key.

There's nothing for an attacker to brute-force in the usual sense: the server doesn't store a secret combination of characters to guess. Login confirmation typically uses device unlocking-like a PIN or biometrics.

For more on how passwordless login works, see our article The End of Passwords: Passwordless Authentication and Digital Security.

Passwords probably won't disappear entirely anytime soon, so classic brute-force defenses remain relevant. But a combination of long, unique passwords, two-factor authentication, and gradual adoption of Passkeys dramatically reduces the scenarios where brute force could ever work.

Conclusion

Brute Force remains one of the most straightforward attack methods: the system systematically checks possible passwords until it finds the right one. But its effectiveness depends heavily on the context. Online brute force is limited by server delays, blockings, CAPTCHA, and suspicious activity analysis, while for offline attacks, password length and the hashing algorithm matter most.

For users, the main protection is a long, unique password for every important service, plus two-factor authentication. Where Passkeys are available, switching to them further reduces reliance on passwords and virtually eliminates brute force as a way to access your account.