# What Is an Infostealer? Protect Your Windows PC | RankShield > An infostealer copies your saved passwords and session cookies to bypass MFA. Here is what an infostealer is, and how to protect your Windows PC from one. > > Source: https://rankshield.co/resources/what-is-an-infostealer-protect-windows-pc/ · RankShield (the verifiable, quantum-safe AI security platform) Resources / Device Security # What is an infostealer, and how do you protect your Windows PC from one? An infostealer runs for a few seconds, copies your saved passwords and session cookies, and leaves. With your session cookie it can walk past your MFA. Here is how it works, and how to defend your PC. July 11, 2026 · 12 min read · infostealer Share An infostealer is malware built to do one thing quietly and fast: copy the valuable data sitting on your Windows PC, above all the passwords, cookies, and session tokens saved in your browser, and send it to an attacker before you notice. It is not dramatic. There is no ransom note and no obvious virus. The program runs for a few seconds, harvests your logged-in life, and exits, often leaving almost nothing behind. It has quietly become one of the most common and damaging attacks on Windows: Flashpoint reported over [1.8 billion credentials stolen in the first half of 2025, an 800% increase](https://flashpoint.io/blog/flashpoint-2025-global-threat-intelligence-index-midyear/) over the prior period, most of it harvested by infostealers. This guide explains what an infostealer is, why it is so dangerous (including how it slips past your multi-factor authentication), how it gets onto a PC, why traditional antivirus often misses it, and how to protect yourself, including how the RankShield Windows app helps. One honest note up front: no tool catches every infostealer, because they are designed to look ordinary and disappear quickly, and no filter is perfect. What good protection does is watch for the behavior that defines the attack, catch a large share of it, and give you a record you can check. Key takeaways - An infostealer is malware that copies the passwords, cookies, session tokens, and crypto data saved on your PC, then exits. Over 1.8 billion credentials were stolen in H1 2025, up 800% (Flashpoint). - The scariest trick is session-cookie theft: with a stolen cookie, an attacker resumes your already-authenticated session and bypasses your MFA. SpyCloud counted 17.3 billion stolen cookies across 2024. - Stolen credentials are now a top way in: they were the initial access vector in 22% of breaches (Verizon 2025 DBIR). - Signature antivirus often misses it because the attack is behavior-driven and frequently fileless: 79% of initial-access attacks in 2024 were malware-free (CrowdStrike). - No tool catches every infostealer; the defense is watching for the behavior itself (a non-browser process reading your browser credential stores), which is what the RankShield Windows app does alongside Microsoft Defender. ## What is an infostealer? An infostealer, short for information stealer, is a type of malware whose whole job is to harvest sensitive data from a computer and send it to an attacker. On Windows, the prize is usually your browser: the saved passwords, autofill data, cookies, and session tokens that Chrome, Edge, Brave, and Firefox store on disk. It will also grab crypto-wallet files, documents, and anything else of value it is told to take. Then it packages that data into a "log" and ships it to the attacker, who uses it or sells it. The stolen logs feed a large criminal marketplace, which is why the volume is so staggering: over [1.8 billion credentials were stolen in the first half of 2025 alone, an 800% jump](https://flashpoint.io/blog/flashpoint-2025-global-threat-intelligence-index-midyear/) (Flashpoint). What makes an infostealer different from the malware people picture is its restraint. It does not lock your files or pop up demands. It runs briefly, takes what it came for, and leaves, often deleting itself, so you may never know it was there until an account is compromised weeks later. Many are sold as a service, so even low-skill criminals can rent one; Red Canary’s 2025 threat report ranked families like [LummaC2 and Rhadamanthys among the top threats it saw](https://redcanary.com/threat-detection-report/trends/info-stealers/), alongside RedLine and StealC. This is the modern shape of PC compromise: quiet, fast, and aimed squarely at your logged-in accounts. ## How does an infostealer bypass your multi-factor authentication? This is the part that surprises people, and it is why infostealers are so damaging: a stolen session cookie can walk straight past your MFA. When you log in and pass your second factor, the website gives your browser a session cookie, a token that says "this person is already authenticated, let them through." That cookie is what keeps you logged in so you do not re-enter your password on every page. An infostealer copies that cookie along with your passwords. The attacker then loads your cookie into their own browser and resumes your authenticated session, without your password and without triggering a fresh MFA prompt, because as far as the site is concerned, you already passed it. The scale of this is not small. SpyCloud counted [17.3 billion stolen session cookies across 2024](https://www.forbes.com/sites/daveywinder/2025/03/19/2fa-code-warning-as-hackers-steal-17-billion-cookies-to-use-in-attacks/), reported by Forbes, many of them valid authentication tokens. This is why "I have MFA turned on" is no longer a complete answer. MFA protects the login moment; it does not protect the session cookie that login creates. Once an infostealer has that cookie, your second factor has already been spent. It also explains why stolen credentials have become a leading way into organizations: Verizon found they were the [initial access vector in 22% of breaches](https://www.verizon.com/about/news/2025-data-breach-investigations-report) in its 2025 report. The defense has to move earlier, to stopping the theft on the device, because once the cookie is gone, the account is exposed. DOWNLOADABLE INFOGRAPHIC ### How an infostealer walks past your MFA A stolen session cookie lets an attacker resume your authenticated session, no password, no fresh MFA. Free to share with attribution. ## How does an infostealer get onto your PC? Almost always because someone was tricked into running it, which is why infostealers spread so widely without any exotic hacking. The classic route is cracked or pirated software and game cheats: the "free" download quietly bundles the stealer. Another huge vector is malvertising and fake download sites, where a search for a legitimate program leads to a poisoned copy. Phishing emails carry them as attachments or links. And a fast-growing trick is the fake fix-it prompt, sometimes called ClickFix, where a bogus CAPTCHA or error tells you to paste a command or press a keyboard shortcut to "verify" or "repair", which actually runs the stealer with your own hands. The through-line is that the malware relies on you to launch it, then works within the normal permissions your account already has. It does not need to break Windows; it just needs a few seconds as you. That is also why it is so egalitarian as a crime: sold as a service for a monthly fee, an infostealer lets someone with little skill run a global credential-harvesting operation. When Microsoft and law enforcement disrupted one such operation, they reported that [Lumma Stealer had infected more than 394,000 Windows computers](https://blogs.microsoft.com/on-the-issues/2025/05/21/microsoft-leads-global-action-against-favored-cybercrime-tool/) in a single two-month window before the takedown. That is the scale one rented tool can reach. ## Why doesn’t my antivirus catch it? Because signature-based antivirus is built to recognize known-bad files, and a modern infostealer is designed to avoid being a known-bad file. Many are fileless or nearly so: they run in memory, use legitimate Windows tools to do their work, and never drop an obvious virus to disk for a scanner to match. The numbers reflect the shift: CrowdStrike found that [79% of attacks to gain initial access in 2024 were malware-free](https://www.crowdstrike.com/en-us/press-releases/crowdstrike-releases-2025-global-threat-report/), meaning there was no malicious file to catch in the first place. Infostealers also change constantly, since a malware-as-a-service operation can recompile to dodge the latest signatures. This does not make antivirus useless; Microsoft Defender and its peers are genuinely strong at what they do, and you should keep them on. It means signatures alone are not enough against this specific, behavior-driven threat. The gap is behavioral: the thing that gives an infostealer away is not a file hash, it is an action, a process that has no business touching your browser suddenly reading the file where your cookies and passwords live. Catching that requires watching behavior, not just scanning files, which is exactly the layer most PCs are missing and the layer built to complement, not replace, your antivirus. ## What are the signs your PC has an infostealer? Infostealers are built to be quiet, so the clues often show up in your accounts rather than on your PC. None of these is proof on its own, but any of them is a reason to act: change passwords, sign out of all sessions, and check the device. - You are signed out of accounts unexpectedly, or see logins from devices and locations that are not yours. - Security emails arrive about sign-ins, password changes, or new devices you did not authorize. - An account is accessed even though you have MFA on and were never prompted, the tell-tale sign of a stolen session cookie. - Your browser saved-password or session behavior changes, or a security tool flags a process reading browser files. - You recently installed cracked software, ran a "fix-it" command from a pop-up, or opened an unexpected attachment, common infection moments. ## How do you protect your Windows PC from infostealers? Protection is a mix of not handing the malware an opening and adding a layer that watches for the theft itself. The steps below work together, and none of them requires you to be a security expert. - Never install cracked, pirated, or "free premium" software or game cheats: these are a leading infostealer delivery method. - Be suspicious of any prompt that tells you to paste a command, press Windows+R, or run something to "verify" or "fix" an error. Legitimate sites never ask that. Close it. - Use a dedicated password manager instead of relying on browser-saved passwords, and turn on the option to require a master password, so your vault is not sitting in the browser store an infostealer targets. - Keep Windows and Microsoft Defender fully updated, and keep Defender turned on: it is a strong first layer. - Sign out of important sessions when done and periodically log out everywhere, which invalidates old session cookies so a stolen one is worthless. - Add a behavioral layer that watches for the infostealer’s defining move, a non-browser process reading your browser credential and cookie stores, so the theft is caught in the act rather than discovered weeks later. THE COVERAGE GAP ### Signature antivirus alone vs a behavioral layer added | | Antivirus alone | Antivirus + behavioral layer | | --- | --- | --- | | Known-bad malware files | Caught well | Caught well | | Fileless / in-memory infostealer | Often missed (79% malware-free) | Watched by behavior | | A process reading your browser cookies | Not inherently flagged | Flagged, the defining move | | When you find out | Often after an account is hit | In the act, with evidence | | What you can show afterward | Little | A verifiable record of what happened | ## How does the RankShield Windows app protect against infostealers? RankShield Security for Windows is built for exactly this threat. It runs alongside Microsoft Defender as a behavioral guardian, and its browser-guard agent watches for the single move that defines an infostealer: a process that is not your browser reaching into Chrome, Edge, Brave, or Firefox to read the login-data, cookie, and session-token stores. That is the moment the theft happens, and catching it in the act is far more effective than discovering the loss weeks later when an account is breached. Sixteen on-device agents cover the wider picture too, credential dumping from memory, fileless scripts seen through the Antimalware Scan Interface, clipboard clippers, ransomware, and boot tampering, and every detection is recorded as a verifiable receipt you can check, with confirmed threats shared as de-identified indicators across the RankShield Network so an attack on one machine helps defend the next. It is free on the [Microsoft Store](https://rankshield.co/windows-security-app/), signed, and runs on Windows 10 and 11. The honest boundary is the same one that runs through this guide. RankShield is not a registered antivirus and does not replace Microsoft Defender; it is a second, behavioral layer that works with it. No tool, RankShield included, catches every infostealer, because they are designed to look ordinary and vanish quickly, and it does not run in the kernel, so it detects and contains behavior rather than blocking every threat inline before it executes. What it realistically does is watch for the browser-credential-theft behavior that most PCs have nothing looking for, catch a large share of it, and give you evidence, all without slowing your machine or replacing the antivirus you already trust. Given that stolen credentials and session cookies are now the currency of modern crime, closing that specific blind spot is the highest-value thing most Windows users can add. See the full app on the [RankShield for Windows](https://rankshield.co/windows-security-app/) page, and protect your other devices with the [device guardian](https://rankshield.co/device-guardian/). ## Is your Windows PC exposed to infostealers? Run this quick check to see how exposed your PC is to the credential and cookie theft infostealers rely on. It weighs your habits, your account hygiene, and whether anything is watching for the theft behavior itself. INFOSTEALER EXPOSURE CHECK ### Is your Windows PC exposed to infostealers? - Do you ever install cracked, pirated, or "free premium" software? - Where do you keep most of your passwords? - Would you know to ignore a pop-up telling you to paste a command to "fix" an error? - Do you periodically sign out of all sessions on important accounts? - Is anything watching for a process reading your browser’s cookie and login stores? FREQUENTLY ASKED ## Questions, answered. ◈ RankShield Assistant · online What is an infostealer in simple terms? ◈ An infostealer is malware that copies valuable data off your computer and sends it to an attacker, then usually exits quietly. On Windows its main target is your browser: the saved passwords, autofill data, cookies, and session tokens stored by Chrome, Edge, Brave, and Firefox, plus crypto-wallet files and documents. It is not like ransomware; there is no ransom note and often no visible sign. It runs for a few seconds, takes what it came for, and may delete itself, so you might not know until an account is compromised. Infostealers are a massive criminal business: over 1.8 billion credentials were stolen in the first half of 2025 alone, up 800% (Flashpoint), most of it harvested by these tools. How does an infostealer get past multi-factor authentication? ◈ By stealing your session cookie rather than your password. When you log in and pass MFA, the website gives your browser a session cookie, a token that proves you are already authenticated so you stay logged in. An infostealer copies that cookie. The attacker loads it into their own browser and resumes your authenticated session without your password and without a fresh MFA prompt, because the site thinks you already passed. SpyCloud counted 17.3 billion stolen session cookies across 2024. This is why MFA alone is no longer a complete defense: it protects the login moment, not the cookie that login creates. Logging out of sessions helps, because it invalidates old cookies, and stopping the theft on the device is the real fix. Why didn’t my antivirus stop the infostealer? ◈ Because signature antivirus is built to recognize known-bad files, and modern infostealers are built to avoid being one. Many run in memory, use legitimate Windows tools, and never drop an obvious virus to disk, so there is nothing for a signature scan to match; CrowdStrike found 79% of initial-access attacks in 2024 were malware-free. They also recompile constantly to dodge signatures. This does not mean antivirus is useless, Microsoft Defender is a strong first layer you should keep on, but it means signatures alone are not enough against this behavior-driven threat. The reliable tell is not a file, it is an action: a process with no reason to touch your browser suddenly reading your cookie and password files. Catching that needs a behavioral layer, not just a scanner. How do infostealers usually infect a computer? ◈ Almost always by tricking someone into running them, then working within the permissions your account already has. The most common routes are cracked or pirated software and game cheats that bundle the stealer, fake download sites and malicious ads that serve a poisoned copy of a real program, phishing attachments and links, and fake fix-it prompts (sometimes called ClickFix) where a bogus CAPTCHA or error tells you to paste a command or press a keyboard shortcut to verify or repair something, which actually runs the malware with your own hands. The common thread is that the malware needs you to launch it. Avoiding pirated software, being suspicious of any prompt that tells you to run a command, and keeping Windows updated remove most of the openings. How can I tell if my PC has an infostealer? ◈ They are built to be quiet, so the signs often appear in your accounts rather than on the PC. Watch for being signed out unexpectedly, logins from devices or locations that are not yours, security emails about sign-ins or password changes you did not make, and, tellingly, an account being accessed even though you have MFA on and were never prompted, which points to a stolen session cookie. On the device, a security tool flagging a process reading browser files, or a recent risky moment like installing cracked software or running a fix-it command, are red flags. If you suspect it, change your passwords, sign out of all sessions to kill stolen cookies, and run a behavioral scan. Because infostealers are stealthy, having something watch for the theft behavior in advance is far more reliable than spotting it after. How does the RankShield Windows app help against infostealers? ◈ RankShield Security for Windows runs alongside Microsoft Defender as a behavioral guardian, and its browser-guard agent watches for the exact move that defines an infostealer: a process that is not your browser reading the login, cookie, and session-token stores of Chrome, Edge, Brave, or Firefox. Catching that in the act is far better than discovering the theft weeks later. Sixteen on-device agents also cover credential dumping, fileless scripts, clipboard clippers, ransomware, and boot tampering, and every detection is a verifiable receipt. It is free on the Microsoft Store and runs on Windows 10 and 11. The honest limit: it is not a registered antivirus and does not replace Defender, it is a second behavioral layer, and no tool catches every infostealer. What it does is close the specific blind spot, browser-credential theft, that most PCs have nothing watching. ## References - [Flashpoint — 2025 Global Threat Intelligence Index, Midyear (1.8B credentials, +800% H1 2025)](https://flashpoint.io/blog/flashpoint-2025-global-threat-intelligence-index-midyear/) - [SpyCloud via Forbes — 17.3 billion stolen session cookies (2024)](https://www.forbes.com/sites/daveywinder/2025/03/19/2fa-code-warning-as-hackers-steal-17-billion-cookies-to-use-in-attacks/) - [Verizon — 2025 Data Breach Investigations Report (22% credentials, 44% ransomware)](https://www.verizon.com/about/news/2025-data-breach-investigations-report) - [Microsoft — Global action against Lumma Stealer (394,000+ infected Windows PCs, May 2025)](https://blogs.microsoft.com/on-the-issues/2025/05/21/microsoft-leads-global-action-against-favored-cybercrime-tool/) - [CrowdStrike — 2025 Global Threat Report (79% of initial-access attacks malware-free)](https://www.crowdstrike.com/en-us/press-releases/crowdstrike-releases-2025-global-threat-report/) - [Red Canary — 2025 Threat Detection Report, infostealers (LummaC2, Rhadamanthys)](https://redcanary.com/threat-detection-report/trends/info-stealers/) - [RankShield — Windows security app (Microsoft Store)](https://rankshield.co/windows-security-app/) ## Make every AI action provable. 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