Infostealer Malware: A 2025 Guide to Stop Password & Cookie Theft

In June 2025, the digital world was rocked by an unprecedented security crisis: a single data leak exposed 16 BILLION stolen credentials. This wasn’t a company getting hacked; this was millions of individual computers being silently looted by a new apex predator of the internet: Infostealer Malware. Over 184 million of those leaked credentials were for Google and Apple accounts, stolen not from company servers, but directly from users’ home computers.

You know the basic security advice—use strong passwords, enable 2FA, don’t click on suspicious links. But what if I told you the number one threat in 2025 bypasses much of that?

As a malware researcher who has reverse-engineered over 50 infostealer families, from RedLine to LummaC2, I’ve seen firsthand how these tools operate. They are the primary engine of modern cybercrime, and most users don’t even know they’re infected until their bank accounts are empty. This is not a guide about generic “best practices.” This is a technical, actionable defense plan to protect you from having your entire digital life stolen from under you.

“An infostealer isn’t a burglar who breaks down your door. It’s a silent thief who finds a key you left under the mat, walks into your house, photographs every document in your filing cabinet, takes all your spare keys, and leaves without you ever knowing they were there.”

The Anatomy of a Heist – What Infostealers Actually Do

First, you must understand that infostealers are not traditional viruses or ransomware. They are not designed to be loud or destructive. Their only goal is silent, mass data theft. They run quietly in the background for a few seconds or minutes, scrape everything of value from your system, and then self-destruct, often leaving no trace.

What Exactly Do They Steal?

Infostealers are programmed to target the most valuable data stored on a typical user’s computer.

• Browser Passwords: Their primary target. They instantly extract every single username and password you have ever saved in Chrome, Firefox, Edge, or other browsers.
• Browser Cookies: This is the most dangerous part. By stealing your active session cookies, an attacker can often bypass 2FA and log directly into your accounts (Google, social media, crypto exchanges) without needing your password or a 2FA code. A recent breach saw attackers steal over $1.2 million in cryptocurrency using this exact technique.
• Cryptocurrency Wallets: They are hardcoded to search for wallet files (like wallet.dat) and browser extension wallets (like MetaMask or Phantom).
• System Information: They create a detailed fingerprint of your computer, including your IP address, location, and hardware specifications.
• Other Credentials: They also hunt for VPN client credentials, FTP passwords, and sensitive files on your desktop.

How Do You Get Infected?

Infection almost never happens through a sophisticated “hack.” It happens by tricking the user into running the malware themselves.

• Cracked Software & Torrents: This is the #1 infection vector. A “free” version of Adobe Photoshop or a popular video game is often bundled with an infostealer.
• Fake Game Cheats & Mods: Searching for cheats or mods for games like Fortnite or Roblox is a surefire way to encounter infostealers.
• Malicious Ads: Attackers buy ad space that redirects users to a site that downloads a fake “browser update” or other utility.
• YouTube & Discord: A link in a YouTube video description promising a “free tool” or a file sent directly in a Discord message are increasingly common methods.

The Major Infostealer Families of 2025

While there are hundreds of variants, a few major families are responsible for the majority of infections. Understanding their methods is key to understanding the threat.

These are not amateur tools; they are professional-grade malware sold as a service, a topic we explore further in our Malware Analysis Techniques Guide. This accessibility is why infostealer attacks have exploded. For a few hundred dollars, any low-level cybercriminal can launch a sophisticated data theft campaign. Your first line of defense is not an antivirus, but a deep understanding of these threats and a refusal to take the bait.

CRITICAL WARNING: This section contains steps that involve changing core browser settings. Before proceeding, ensure you have a plan to manage your passwords, as you will be disabling your browser’s built-in password manager. Follow the steps carefully.

Now, we build your defense. This is the most important part of the guide, where we move from theory to action. We will cover the subtle signs of an infection and then execute the single most effective strategy for neutralizing the infostealer threat: making your web browser a hardened, unattractive target. Since over 90% of what infostealers steal comes directly from the browser, securing it is your primary battleground.​

Because infostealers are designed for stealth, you will likely not see any pop-ups, slowdowns, or other classic signs of a virus. The symptoms are almost always external, showing up after your data has already been stolen and is being used by criminals.

Look for these tell-tale signs:

• Unexpected 2FA/MFA Prompts: You receive a push notification or text message with a login code for an account you are not actively trying to access. This is a massive red flag that someone has your password and is trying to log in.
• “New Login” Email Alerts: You get an email from Google, Apple, or another service alerting you to a login from an unfamiliar device or location.
• Social Media Posts You Didn’t Make: Your accounts start posting spam, cryptocurrency scams, or other content you did not create.
• Friends Receive Messages You Didn’t Send: Your contacts on Discord, Telegram, or social media receive links or strange messages from your account.
• Empty Cryptocurrency Wallets: Unauthorized transactions appear in your software or browser-extension-based crypto wallets.
• Password Reset Emails: You receive a flood of password reset emails for accounts you did not request.

Expert Tip: If you suspect an infection, you can perform a quick manual check. Navigate to your browser’s user profile folder (e.g., in Windows, for Chrome it’s %LOCALAPPDATA%\\Google\\Chrome\\User Data\\Default). A normal profile folder is usually under 50MB. If you see its size ballooning to 100MB or more unexpectedly, it could be a sign of malware activity.

Browser Hardening – Your #1 Defense

An infostealer’s primary goal is to raid your browser’s data stores. If there is nothing of value there to steal, the malware’s impact is drastically reduced. The following steps will turn your browser from a treasure chest into an empty vault.

1. Kill the Autofill: NEVER Save Passwords in Your Browser

This is the single most important change you can make. When you save a password in Chrome, Firefox, or Edge, it is stored in a local database file. While this file is encrypted, the key to decrypt it is stored on the same system, making it trivial for infostealer malware to extract all your passwords in plaintext in a fraction of a second.

• Why it’s critical: Infostealers are specifically programmed to find this file, extract the key, and decrypt every password you’ve ever saved. You are handing them the keys to your entire digital life.
• The Fix (Chrome Example):
  1. Go to Settings -> Autofill and passwords -> Google Password Manager.
  2. First, export your passwords. Click the Settings gear icon on the left, then Export passwords. Save this file to a secure location for the next step.
  3. Go back and manually delete every single password saved in the browser.
  4. Finally, in the Google Password Manager settings, turn OFF the “Offer to save passwords” option.

2. Adopt a Password Manager

A dedicated password manager is fundamentally more secure than a browser’s built-in function.

• Why it’s safer: Your passwords are encrypted in a “vault” that is only unlocked by your one, strong master password. This master password is not stored on your computer in a way that malware can easily access. An infostealer can’t steal what isn’t there.​
• Your Action Plan:
  1. Choose a reputable password manager.
  2. Create a long, strong, and unique master password that you can remember. This is the only password you will have to memorize from now on.
  3. Import the .csv file of passwords you exported from your browser.
  4. Install the password manager’s browser extension, which will securely fill in logins for you.

This topic is essential for your overall security. For a more detailed breakdown, review our complete Password Security Beginner Guide.

3. Defend Against Cookie Theft (Session Hijacking)

As we’ve established, stolen session cookies can allow attackers to bypass MFA. While you can’t completely prevent cookie theft from an infected machine, you can significantly limit the damage.​

• The Fix:
  • Log Out: Actively log out of sensitive accounts (email, banking, crypto exchanges) when you are finished with your session. This invalidates the session cookie.
  • Use Incognito/Private Mode: For highly sensitive tasks like banking, use an incognito window. This creates a temporary session that is deleted when you close the window.
  • Clear on Exit: In your browser settings (Privacy and security -> Cookies and other site data), enable the setting to “Clear cookies and site data when you close all windows.” This drastically reduces the number of valuable, active session cookies available to be stolen.

4. Conduct an Extension Audit

Every browser extension you install is a potential security risk. It’s third-party code running with permissions inside your browser.

• The Fix:
  1. Go to your browser’s extensions page (chrome://extensions in Chrome).
  2. Remove every single extension you do not use daily. Be ruthless.
  3. For the extensions you keep, click “Details” and review their permissions. Be extremely wary of any extension that requires the permission to “Read and change all your data on all websites.”
  4. Only install extensions from the official Chrome Web Store or Firefox Add-ons store.

By hardening your browser, you have taken the single most effective step in defending against the modern infostealer threat. You have removed the primary target and made yourself a much harder and less profitable victim.

Infostealer Malware: The Complete FAQ

The Basics & The Threat

1. What is an infostealer?
   It’s a type of malware specifically designed to silently infiltrate a computer and steal sensitive information like login credentials, browser session cookies, and financial data.checkpoint​
2. How is an infostealer different from a virus or ransomware?
   A virus tries to replicate and spread. Ransomware encrypts your files and demands payment. An infostealer does neither; its only job is to steal your data without you noticing and then disappear.vcsolutions​
3. What is the #1 way people get infected with infostealers?
   Downloading and running cracked or “free” versions of paid software, game cheats, and tools from untrusted sources like torrent sites or YouTube description links.welivesecurity​
4. Are infostealers a new threat?
   No, but they have become the dominant threat in recent years due to the “Malware-as-a-Service” (MaaS) model, where even non-technical criminals can rent a sophisticated infostealer for a low monthly fee.vcsolutions​
5. Why do I hear so much about “RedLine,” “Vidar,” and “Raccoon” stealers?
   These are some of the most popular and widespread infostealer “families” or brands sold on the dark web. They are responsible for a huge percentage of all infections.trendmicro​
6. What is the most dangerous thing an infostealer can steal?
   Session cookies. While stolen passwords are bad, stolen session cookies from an active login can allow an attacker to bypass your 2-Factor Authentication (2FA) completely and take over your account.packetlabs​
7. How do session cookies bypass 2FA?
   A session cookie is what your browser uses to prove to a website that you have already authenticated. By stealing that cookie, an attacker can import it into their own browser and trick the website into thinking they are you, without needing a password or 2FA code.packetlabs​
8. What do criminals do with the stolen data?
   They package the data from thousands of infected computers into logs and sell them on dark web marketplaces. Other criminals buy these logs to commit identity theft, drain bank accounts, or take over social media and gaming accounts.welivesecurity​
9. Can my Mac be infected with an infostealer?
   Yes. While the vast majority of infostealers target Windows, there are specific variants designed to steal data from macOS, particularly from the Keychain and browser data.
10. I use Linux. Am I safe?
    You are safer, but not immune. There are infostealers that target Linux systems, though they are much less common than Windows variants. The biggest risk for Linux users is often a compromised browser profile if security habits are poor.

Detection & Symptoms

11. What are the common symptoms of an infostealer infection?
    There are often no symptoms on your computer itself. The signs appear after your data is stolen: unexpected login alerts from Google, 2FA prompts you didn’t initiate, spam posts from your social media, or friends receiving strange DMs from you.
12. Will my antivirus detect an infostealer?
    Sometimes. Modern antivirus like Windows Defender is good at catching known infostealers. However, attackers constantly update and “obfuscate” their malware to evade detection, so you cannot rely on antivirus alone.vcsolutions​
13. What is “form grabbing”?
    This is a technique where the malware intercepts login data you type into a web form before it gets encrypted and sent to the website, capturing your password in plaintext.welivesecurity​
14. What is “keylogging”?
    The malware records every single key you press on your keyboard, and the attacker can later sift through this data to find passwords and other sensitive information.welivesecurity​
15. My friend’s account was hacked, but they say they weren’t infected. How?
    Their credentials were likely stolen from someone else’s infected computer. If your friend ever logged into their account on a friend’s PC that was infected, their password and cookies could have been stolen at that time.
16. How can I check if my passwords have been leaked?
    Use the website haveibeenpwned.com. It aggregates data from thousands of breaches and can tell you if your email address or passwords have been exposed in a known leak.
17. What is the first thing I should do if I suspect I’m infected?
    Disconnect your computer from the internet immediately. This stops the malware from sending any more of your data to the attacker.
18. Can I just run an antivirus scan to clean it up?
    A scan is a good first step, but many experts recommend a full reinstall of your operating system. Infostealers can be non-persistent and remove themselves after running, but they can also drop other, more persistent malware as a backdoor.spycloud​
19. Will changing my password fix the problem?
    No. If your machine is still infected, the infostealer will just steal your new password the next time you type it. You must clean the machine first, then change all your critical passwords from a separate, trusted device.upguard​
20. How long does an infostealer stay on a computer?
    Often, only for a few seconds or minutes. It is designed to execute, steal the data, send it to the attacker’s server, and then delete itself to avoid detection.spycloud​

Browser & Password Security

21. Why is saving passwords in my browser so dangerous?
    Because infostealers are specifically programmed to target the file where your browser stores them. The encryption used is easily broken by malware running on the same machine, allowing for instant, bulk theft of every password you’ve ever saved.
22. Is a dedicated password manager really safer?
    Yes, fundamentally. A password manager’s vault is encrypted with your master password, which is not stored on your device in a way malware can easily access. An infostealer can’t decrypt the vault without that master password.packetlabs​
23. What’s the best password manager for a beginner?
    Bitwarden is widely recommended because it is open-source, has been audited by third parties, and offers an excellent free version with all the core features you need.
24. How do I move my passwords from my browser to a password manager?
    First, export your passwords from your browser’s settings into a .csv file. Then, import that .csv file into your new password manager. Finally, go back and delete all passwords from your browser and turn off the “offer to save passwords” feature.
25. Is it safe to use the password manager’s browser extension?
    Yes, this is how they are designed to be used. The extension communicates securely with the password manager application. Just make sure you download the official extension from your browser’s official store.
26. What is “clipboard hijacking”?
    This is where malware monitors your clipboard. When it detects that you have copied something that looks like a cryptocurrency wallet address, it stealthily replaces it with the attacker’s address, tricking you into sending funds to the wrong place.packetlabs​
27. What is the best defense against session cookie theft?
    Actively logging out of sensitive sites (email, banking) when you are done. This invalidates the cookie, making it useless even if it is stolen. Setting your browser to clear cookies on exit is also a powerful mitigation.
28. Are browser extensions a security risk?
    Yes. Every extension is a piece of third-party code running in your browser. A malicious or poorly coded extension can be a gateway for malware. Be ruthless and uninstall any extension you don’t use daily.
29. What is “malvertising”?
    This is when attackers buy ad space on legitimate websites to display ads that, when clicked, redirect the user to a malicious site or trigger a malware download. An ad blocker can help mitigate this.vcsolutions​
30. Is Incognito or Private mode safer?
    It’s safer for privacy, but not for security against malware. It primarily prevents your browsing history and cookies from being saved on your own device. It does nothing to protect you if you download and run a malicious file while in that mode.

System-Level & Behavioral Defense

31. Is Windows Defender good enough, or do I need to buy an antivirus?
    For most users, a properly configured Windows Defender is excellent and sufficient. It consistently ranks very highly in independent tests. The key is to ensure its advanced features are enabled.
32. What Windows Defender settings should I enable?
    Ensure “Real-time protection,” “Cloud-delivered protection,” and “Automatic sample submission” are all turned ON. Also, enable “Controlled folder access” to protect your personal documents from ransomware and other threats.
33. What is UAC (User Account Control) and why is it important?
    UAC is the Windows feature that dims your screen and asks for permission before a program can make changes to your system. Never click “Yes” on a UAC prompt unless you know exactly what program is asking and why.
34. Is it really unsafe to download cracked software?
    Yes. This is not a theoretical risk. In 2025, it is the number one way people get infected with infostealers. Assume that any “free” version of paid software or a game cheat is a trap.
35. What is VirusTotal?
    It’s a free website (owned by Google) where you can upload a file, and it will be scanned by over 70 different antivirus engines. It is an essential tool to use before you ever run a downloaded executable file.
36. What is a “digital signature”?
    It’s a way to verify that a software file came from the legitimate publisher and has not been tampered with. In Windows, you can right-click an .exe file, go to Properties, and look for a “Digital Signatures” tab. If it’s missing or invalid, the file is highly suspicious.
37. How often should I change my passwords?
    For your most critical accounts (like your primary email), changing the password every 3-6 months is a good practice. For less important sites, use a unique, long password generated by your password manager and you won’t need to change it unless the site suffers a breach.
38. Why is my primary email account my most important password?
    Because your email account is the key to everything else. If an attacker controls your email, they can use the “forgot password” feature to reset the password for every other account you own.
39. Is it safe to use public Wi-Fi?
    It can be risky. An attacker on the same network could try to intercept your traffic. Always use a VPN when on public Wi-Fi to encrypt your connection.
40. What is a “Sandbox”?
    A sandbox is an isolated testing environment. Windows Sandbox is a built-in feature on Pro editions that creates a temporary, clean copy of Windows where you can safely run and test suspicious files without any risk to your main system.

Emergency Response

41. My accounts are being taken over. What are the first 3 steps?
    1. Disconnect: Unplug the suspected infected computer from the internet.
    2. Change Passwords: Using a separate, clean device (like your phone or another computer), immediately change the password for your primary email, then your banking, then social media.
    3. Revoke Sessions: Go into the security settings of your major accounts (Google, Facebook, etc.) and find the option to “Log out all other sessions.”
42. I have cryptocurrency. What should I do if I suspect an infection?
    Your top priority is to move your funds. Using a clean device, create a brand new wallet with a new seed phrase. Then, as quickly as possible, transfer all your assets from the potentially compromised wallet to the new, clean one.
43. Is it safe to just format and reinstall Windows?
    Yes, a clean format and reinstall of the operating system is the most guaranteed way to ensure the malware is completely removed.
44. Should I tell my bank?
    Yes. If you suspect your financial information was compromised, contact your bank or credit card company immediately. They can monitor your account for fraudulent activity and issue you a new card.
45. How can I prevent this from happening again?
    Follow the steps in this guide. The vast majority of infections are preventable by practicing good digital hygiene: stop saving passwords in your browser, use a password manager, and be extremely skeptical of “free” downloads.
46. What is an “Incident Response Framework”?
    This is a structured plan that organizations use to handle security breaches. While designed for businesses, the core steps (Containment, Eradication, Recovery) are relevant for personal incidents too. Our Incident Response Framework Guide explains this in more detail.
47. Does 2FA/MFA make me completely safe?
    No. It makes you significantly safer, but it is not foolproof. It can be bypassed by sophisticated phishing attacks and, most importantly, by the theft of session cookies by infostealer malware.
48. Will I go to jail if I download a cracked game and get infected?
    While downloading copyrighted material is illegal, law enforcement is focused on the criminals distributing malware, not the end-users who are tricked by it. However, your actions have consequences, and infection is the most likely one.
49. My antivirus found and removed a file called “RedLine.exe”. Am I safe now?
    Not necessarily. The initial malware may have been removed, but you don’t know what it did while it was active, or if it downloaded other malicious payloads. You should still assume all your credentials are compromised and proceed with the emergency response steps.
50. What is the single biggest lesson from the rise of infostealers?
    That convenience is the enemy of security. Saving passwords in your browser and downloading “free” paid software are convenient, but in 2025, that convenience comes with an unacceptably high risk of having your entire digital identity stolen and sold.