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When you hear that an account got hacked, it is tempting to imagine one dramatic moment where a villain breaks a lock and slips inside, but most real-world account break-ins look more like patient, repetitive guessing or quiet reuse of something that was already stolen. The tricky part for new defenders is that different credential attacks can look similar at first glance because they all involve someone trying to become you in a system. The purpose of this lesson is to help you tell four common credential attack types apart by the clues they leave behind and the thinking that drives them. We are going to keep it high-level and beginner-friendly, but still practical enough that you can listen to a short description of suspicious login activity and immediately sort it into the right bucket. Once you can name the pattern correctly, you can also predict the likely next move and the kind of damage that follows, which is exactly the kind of decision-making that matters for incident response.

Before we split the attack types, it helps to ground ourselves in what a credential really is and why it is such a powerful target. A credential is proof, accepted by a system, that you are allowed to act as a particular identity, and that proof can be something you know, something you have, or something you are. The most familiar example is a username and password pair, but modern systems often add a second step like a one-time code or a push approval, which is called Multi-Factor Authentication (M F A) when more than one factor is used. Attackers go after credentials because they are a shortcut that bypasses many other defenses, since a successful login looks like normal use. Even if a system has strong security settings, a valid login can still open the door, especially if that account has access to email, finance, admin tools, or sensitive files. Once you see credentials as a universal key that works across many systems, it becomes easier to understand why attackers invest so much effort in trying different ways to obtain them.

Now we can define the four credential attack categories you will hear about again and again. Credential stuffing is when an attacker takes username and password pairs stolen from one place and tries them on another place, betting that people reused the same password. Password spraying is when an attacker tries a small set of very common passwords against many accounts, aiming to avoid lockouts while still finding weak choices. Brute force is when an attacker tries many possible passwords for a particular account or a small set of accounts, pushing volume until something works or defenses stop them. Credential theft is the broader idea of stealing the credential itself, such as through phishing, malware, social engineering, or interception, so the attacker logs in using the real secret rather than guessing. Even in those simple definitions, you can hear the difference in strategy: stuffing reuses known pairs, spraying uses a few guesses across many identities, brute force focuses many guesses on one identity, and theft focuses on obtaining the real secret by tricking or compromising the user or device.

Credential stuffing is easiest to understand if you picture it as recycling, because the attacker is not inventing passwords but reusing ones that already worked somewhere else. The typical starting point is a pile of leaked credentials from a previous breach, and that pile may contain millions of pairs. The attacker then tests those pairs against a different service such as email, shopping, streaming, or corporate login portals, hoping to find people who reused passwords. The important clue is that the attacker already has both the username and the password for each attempt, so each login attempt is a full pair. That means the attempts often look like a large number of different accounts being tried, with one or a few attempts per account, because the attacker is checking whether that exact pair works. Another clue is that the attempts can arrive in waves, sometimes from many different network locations, because attackers spread the traffic to avoid being blocked. The core risk of stuffing is not that someone chose a weak password, but that someone reused a password that used to be secret but is not secret anymore.

Password spraying has a different feel because the attacker is betting on the most predictable human choices. Instead of having a list of stolen pairs, the attacker usually has a list of valid usernames, which can be guessed from company email formats, public staff pages, or other sources. The attacker then tries a small number of passwords that are popular or seasonally common, such as a company name plus a year, a simple pattern, or a default choice people use when rushed. The key idea is that the attacker wants to avoid account lockouts, so they do not hammer one account with repeated guesses. Instead, they try one password across many accounts, wait, then try a second password later, keeping the number of guesses per account low. If you watch logs, spraying often shows the same password being attempted for many different users, often spread across time to look less suspicious. The risk here is about predictable password behavior at scale, where even if only a small fraction of users pick weak passwords, that small fraction can still be enough for attackers to gain a foothold.

Brute force is the more classic idea people imagine, and it is the most direct form of guessing. In brute force, the attacker targets an account and tries many password possibilities until something works, often starting with common guesses and moving toward more combinations. This might be done with a single account, especially if the attacker believes it has high value, or with a small set of accounts that are likely to have elevated privileges. The hallmark clue is repeated failed login attempts for the same username, often at a high rate, sometimes escalating in speed as the attacker automates the attempts. In a well-protected environment, brute force is usually noisy and tends to trigger defenses like lockouts, rate limits, or alerts, which is why many attackers prefer spraying when they want to stay subtle. Still, brute force can succeed in places with weak protections, especially where there is no lockout policy, where remote access is exposed, or where a forgotten legacy system is still reachable. The risk in brute force is that volume can beat weak secrets, and weak protections can give the attacker unlimited tries.

Credential theft is different because it is not primarily about guessing, even though it might be combined with guessing later. Theft means the attacker gets the credential through compromise, such as tricking the user into typing it into a fake login page, capturing it with malware, stealing it from a password manager that is unlocked, or intercepting it through a compromised device or network path. Phishing is a common method, where the attacker sends a message that looks legitimate and lures the user into revealing the password or approving an M F A prompt they did not initiate. Another form is stealing session tokens, which are pieces of data that prove you are already logged in, allowing an attacker to act as you without knowing your password. The clue here is that the login might actually succeed on the first try, because the attacker is using valid information, and the activity may look normal until you notice odd locations, devices, or actions. Theft can also involve insiders or physical access, where someone sees a password on a note, overhears it, or obtains it from an unlocked workstation. The risk is high because theft often bypasses password strength entirely and can defeat some defenses if the attacker steals something that represents an already authenticated session.

To differentiate these attacks reliably, it helps to practice thinking in terms of inputs, targets, and patterns over time. Ask yourself what the attacker likely has at the start: a list of stolen username and password pairs, a list of usernames only, the ability to generate many guesses, or a way to trick someone into giving up secrets. Then ask how the attacker applies that: one attempt per account across many accounts suggests stuffing, one password tried across many users suggests spraying, many attempts against one user suggests brute force, and a clean successful login following a suspicious message or device compromise suggests theft. Also pay attention to what defenders see first, because the earliest signs differ. Stuffing and spraying often show many failed logins spread out across accounts, while brute force shows concentrated failures on one account. Theft might show fewer failures and more odd successful activity, sometimes paired with a sudden shift like an unfamiliar device or a new email forwarding rule.

It is also important to understand how M F A changes the game, because beginners often assume it makes credential attacks disappear. M F A can significantly reduce the success of password guessing and password reuse, but it does not automatically stop everything. Credential stuffing and spraying can still identify which accounts have valid passwords, even if M F A blocks full access, and that knowledge can be valuable for attackers who then move to social engineering. Brute force can still succeed where M F A is not enabled or where a system uses weaker second factors, like easily intercepted codes or poorly secured recovery options. Credential theft can sometimes defeat M F A through phishing that captures one-time codes in real time, through push fatigue where a user approves prompts to make them stop, or through stolen session tokens that bypass the need to authenticate again. So the presence of M F A changes the probability of success and the attacker’s follow-on choices, but it does not erase the need to recognize which method is being attempted.

A useful way to make these distinctions stick is to imagine four different attacker mindsets, because each one makes different tradeoffs between stealth, speed, and effort. The credential stuffer is an optimizer who already has data and wants quick wins by testing it widely, treating your organization as just one more place to try. The password sprayer is a patient gambler who assumes at least a few people chose something weak and tries to slip under lockout thresholds. The brute forcer is a battering ram, loud and persistent, often relying on poor defenses or hoping nobody is watching. The credential thief is a pickpocket who wants to take the real key from your pocket, sometimes without you noticing until later. Thinking this way helps you predict what comes next, because each mindset has a typical next step, like moving laterally after a single success, or switching tactics if they hit M F A barriers.

Beginners also benefit from understanding why these attacks often appear together in a single incident, because real attackers are flexible and will mix methods. An attacker might start with password spraying to find one weak account, then use that access to gather more usernames, and then run a targeted brute force attempt against a privileged account they discovered. Another attacker might run credential stuffing on an external portal and, after getting a valid password that is blocked by M F A, pivot to phishing that user to capture the second factor. Credential theft might happen first through phishing, and once inside, the attacker may steal stored credentials or session tokens to expand access without more guessing. This matters because you may see multiple patterns in your logs and assume they are unrelated, when they are actually stages of the same campaign. Recognizing the core method in each stage helps you describe what is happening clearly and choose defenses that match the attacker’s current approach.

There are also common misconceptions that can trip you up if you do not correct them early. One misconception is that credential stuffing is the same as brute force because both involve repeated login attempts, but stuffing is about testing known pairs, while brute force is about guessing unknown passwords. Another misconception is that spraying is just a slower brute force, but the real difference is the distribution of guesses across many accounts to avoid lockouts. A third misconception is that credential theft always requires malware, when in fact simple social engineering and convincing fake login pages can be enough. Finally, some people assume that if logins come from many network locations, it must be many attackers, but attackers can easily distribute their traffic through rented infrastructure or compromised systems. Clearing up these misconceptions helps you stay calm and precise, because good incident response depends on naming the pattern correctly rather than reacting to the most dramatic interpretation.

You can also use impact clues to help differentiate the method, because each attack type tends to produce a different kind of harm. Credential stuffing often results in account takeovers that look like normal user activity, and the attacker may immediately perform actions that monetize access, like changing shipping addresses, redeeming stored value, or harvesting personal information. Password spraying often results in one or a few compromised accounts, and those accounts may be used as an entry point for broader intrusion, especially if the environment has single sign-on or shared access. Brute force may cause noticeable disruption because accounts get locked, login systems get overloaded, and users complain, even if the attacker never succeeds. Credential theft often leads to the most dangerous outcomes because the attacker may have high confidence in their access and may operate for longer before detection, especially if they obtained not just a password but also email access, session tokens, or recovery options. When you combine the pattern in the logs with the kind of impact you see, your confidence in the diagnosis improves.

To make all of this feel more real, imagine a simple scenario with an online service used by many people in a school or a small company. If you see thousands of different usernames each failing once or twice, and then a handful succeed, that aligns with credential stuffing because it looks like testing known pairs across many accounts. If you see one password attempted for hundreds of usernames, then later a second password attempted for those same usernames, that aligns with spraying because it shows the attacker distributing guesses to avoid lockouts. If you see one username getting hammered with dozens or hundreds of attempts in a short period, that aligns with brute force because the attempts are concentrated on a single identity. If you see a user report a suspicious message and soon after their account logs in successfully from an unfamiliar device and starts sending messages or changing settings, that aligns with credential theft because the attacker likely tricked the user or captured a valid session. You do not need advanced tools to reason about these patterns; you just need the habit of matching the observed behavior to the attacker’s starting resources and strategy.

As you build your instincts, keep the defender’s goal in mind, which is not only to stop the current attempt but to reduce the chance of repeat success. For credential stuffing, the long-term fix is to break password reuse and detect reused credentials quickly, because the attacker is relying on old leaks and human habit. For password spraying, the long-term fix is to reduce predictable passwords, enforce stronger policies, and use protections that make low-and-slow guessing ineffective. For brute force, the long-term fix is strong rate limiting, lockout policies tuned to avoid abuse, and monitoring that notices repeated failures before they become outages. For credential theft, the long-term fix is to make phishing and token theft harder through user awareness, strong authentication flows, and safeguards around session management and recovery. Even though we are not doing implementation steps here, it is still valuable to link each method to the category of defense it pressures, because that connection makes the method easier to remember and easier to explain under pressure.

As a final wrap-up, the whole point of differentiating stuffing, spraying, brute force, and theft is to turn a vague idea of someone trying to log in into a clear story about what the attacker has, what they are trying, and what they will likely try next. Credential stuffing is about reusing stolen pairs across many accounts, often with few attempts per account, betting on password reuse. Password spraying is about trying a few common passwords across many users, carefully avoiding lockouts while searching for the weakest links. Brute force is about hammering one account or a small set with many guesses, loud and persistent, and often stopped by basic protections when they are in place. Credential theft is about obtaining the real secret or session proof through trickery or compromise, leading to successful logins that can look normal until you notice the context. When you can sort an incident into the right category quickly, you can respond with clearer communication, better prioritization, and fewer wrong assumptions, which is exactly the kind of calm, structured thinking this certification is trying to build.