The Rise of Infostealers: How Modern Malware Steals Your Passwords, Cookies, and Credit Cards—and How to Stop It

ByInnoVirtuoso

You log in, your bank welcomes you, and everything looks normal. But behind the scenes, a silent thief may already have what it needs: your saved passwords, your browser cookies, and your autofill data. No alarms. No locked screen. Just a quiet handoff of your digital life to strangers.

That’s the unsettling reality of infostealers—fast-growing malware built to grab the keys to your online identity and finances. These aren’t clunky viruses from the early 2000s. They’re sleek, targeted, and often delivered through legitimate-looking ads or installers. And once your data is siphoned off, it’s sold as “logs” on underground markets, reused to hijack sessions, or leveraged to pivot into your work accounts.

If that sounds devastating, here’s the good part: with a few smart moves, you can dramatically reduce your risk. Let’s break down how infostealers work, what makes them so dangerous (especially stolen cookies), and the concrete steps you can take today to stay safe.

What Is an Infostealer? (And Why It’s Exploding Right Now)

An infostealer is a type of malware designed to grab sensitive information from your device and send it to attackers. Think of it like a vacuum cleaner for your digital life. It scans your system for high‑value data and sucks it up—fast.

Most infostealers target: – Browser-saved passwords and autofill data – Session cookies and tokens (used to keep you logged in) – Credit card details stored in browsers – Crypto wallets, VPN credentials, and messaging app tokens – Gaming accounts, email, and work platforms

Here’s why that matters: many people now keep everything in their browser. Passwords. Payment methods. Even persistent sessions that don’t require logins for months. Infostealers turn that convenience into a goldmine.

They’re also easy to deploy. Criminals rent them as “malware-as-a-service,” push them through fake ads or cracked software, and sell stolen data in bulk. As a result, infostealers have become a go-to tool for both opportunists and sophisticated attackers.

If you want a deeper, technical map of how attackers target browser stores and tokens, see MITRE ATT&CK for “Credentials from Web Browsers” T1555.003 and “Input Capture” T1056.

How Infostealers Work: From Infection to Exfiltration

Infostealers follow a simple playbook. The magic is in how quiet and fast it is.

Step 1: Infection Vectors You Actually See Every Day

Attackers don’t need zero-days to get in. They use social engineering and trusted channels: – Malvertising: Sponsored search ads that look like real software (Zoom, Notepad++, OBS), but link to fake sites. Microsoft has documented large-scale campaigns delivering stealer malware via malicious ads and SEO poisoning (Microsoft Security Blog). – Fake installers and updates: Trojanized downloads for popular tools. These often come from lookalike domains or typo-squats. – Cracked software: “Free” versions of paid apps. You pay with your data. – Phishing emails or DMs: Attachments or links that drop a small loader, which pulls the infostealer next. – Imposter browser extensions: “Productivity” add-ons that ask for overbroad permissions.

Once you click, the malware runs in memory or drops a small executable. From there, it hunts.

Step 2: What They Target, Specifically

Infostealers scan local browser profiles and system directories, including: – Password managers built into browsers – Cookies and session tokens – Autofill data (names, addresses, credit card numbers) – Saved payment methods – Crypto wallets and browser extension wallets – Clipboard contents (especially crypto addresses)

They’re optimized for Chrome, Edge, Brave, and other Chromium-based browsers, but they also target Firefox and, increasingly, Safari on macOS. For the technically curious, this aligns to credential access tactics in MITRE ATT&CK’s “Credentials from Password Stores” T1555.

Let me explain why that’s dangerous: an attacker doesn’t need your actual username and password if they can steal your session token or cookie. It’s like swiping your visitor badge at the office—no need to ask the receptionist again.

Step 3: Exfiltration and Monetization

Infostealers bundle your data into “logs” and send them out—often via encrypted channels or messaging platforms like Telegram. From there, the data: – Gets sold wholesale on underground markets as “fullz” (full identity kits) – Enables account takeovers and session hijacking – Becomes ammo for spear-phishing or business email compromise – Fuels financial fraud or crypto theft

One notorious marketplace, Genesis Market, specialized in selling device fingerprints and session cookies to help bypass security. It was taken down in a global law enforcement operation nicknamed “Operation Cookie Monster” (Europol, KrebsOnSecurity). The takedown made a dent, but dozens of copycats exist.

Why Stolen Cookies Are So Dangerous: Session Hijacking 101

Password theft is bad. Cookie theft can be worse. Here’s why.

What Is a Session Cookie?

When you log in, a website issues a session token (often stored in a cookie). This tells the site, “Yes, this is still you,” so you don’t have to re-enter your credentials every click. It’s meant to be convenient.

How Attackers Use Stolen Cookies to Bypass MFA

If malware steals that token, an attacker can replay it and appear logged in as you—no password required, and often no MFA prompt. This is called “pass-the-cookie,” and it can give attackers immediate access to email, banking, or corporate tools.

  • Cloudflare’s primer on session hijacking is a good, quick read: What is session hijacking?
  • Google has proposed “Device Bound Session Credentials” to bind tokens to hardware, which would kill the value of stolen cookies (Google Security Blog).

Here’s why that matters: even if you use strong passwords and MFA, a stolen session can cut in line. That’s why detection and forced reauthentication matter so much.

How Do You Kick Out an Attacker Using Your Cookie?

  • Sign out of all sessions from the account’s security settings.
  • Change your password from a clean device.
  • Revoke OAuth tokens and app authorizations you don’t recognize.
  • If it’s a work account, ask IT to revoke tokens and invalidate sessions at the identity provider.

Real-World Infostealer Families and Campaigns

Infostealer “brands” come and go, but the playbook stays effective. A few you may hear about: – RedLine Stealer: A prolific stealer sold on underground forums. Distributed via malvertising and cracked software. – Raccoon Stealer 2.0: Returned with a rebuilt codebase after law enforcement disruptions. Often spread via fake installers and SEO poisoning (ESET WeLiveSecurity). – Vidar and Lumma: Known for stealing browser data, crypto wallets, and system info, and exfiltrating to Telegram. – Aurora: Another stealer often sold as a service to affiliates. – Atomic macOS Stealer (AMOS): Targets macOS users via fake installers, harvesting keychain items, passwords, and crypto (Kaspersky Securelist).

Researchers and vendors routinely publish deep dives on distribution tactics such as malvertising and SEO poisoning—these are well worth a read if you manage teams or budgets for security (Microsoft Security Blog, Sophos News).

How to Protect Yourself (and Your Organization) from Infostealers

You don’t need to be a security pro to block most infostealers. But you do need to be intentional. Here’s a layered plan that works in real life.

For Individuals and Families

Start with the basics. They go a long way.

  • Only download software from official sources
  • Type the URL yourself or use bookmarks.
  • Avoid “sponsored” results for software in search engines. Go directly to the vendor site.
  • Keep your system and apps updated
  • Enable automatic updates for your OS and browsers.
  • Use a dedicated password manager (not the browser’s save feature)
  • It’s easier to audit and export. It also helps you avoid reusing passwords.
  • Use unique, long passwords everywhere.
  • Turn on strong MFA—ideally security keys or passkeys
  • App-based TOTPs are good. Physical security keys or passkeys are better and more phishing-resistant (NCSC UK on passkeys, FIDO Alliance).
  • Be cautious with browser autofill and stored cards
  • Consider disabling card storage in browsers. If you keep it, add an extra verification step.
  • Separate your “risky” browsing
  • Use one browser profile for banking and sensitive services, and another for general browsing and downloads. Think of it like two separate kitchens.
  • Clear persistent sessions on sensitive accounts
  • Log out periodically or after important actions (banking, crypto).
  • Use reputable endpoint protection
  • A good antivirus/EDR can catch many known stealers. Keep signatures current.
  • Watch for signs you’ve been compromised
  • Sudden password resets, unfamiliar logins, or new sign-in alerts. Check dashboards for “devices” and “recent activity.”
  • Monitor email for breach alerts and consider credit protections
  • Use Have I Been Pwned to see if your email appears in known breaches.
  • If money or identity data is exposed, consider a credit freeze (FTC guidance).

For Teams and Organizations

You can reduce risk without boiling the ocean. Prioritize controls that block how stealers land and exfiltrate.

  • Block malvertising and shady downloads
  • Use DNS filtering and SafeSearch enforcement.
  • Consider application allowlisting for managed endpoints.
  • Harden browsers and password storage
  • Disable browser password saving for corporate profiles. Require dedicated password managers with enterprise policies.
  • Enforce phishing-resistant MFA
  • Favor FIDO2 security keys or passkeys for SSO/MFA. Add conditional access and device compliance checks where possible.
  • Shorten session lifetimes and rotate refresh tokens
  • Force periodic reauth for sensitive apps. Invalidate tokens on risky sign-ins. Follow best practices in the OWASP Session Management Cheat Sheet.
  • Detect and respond to stealer activity
  • Monitor for unusual login patterns, cookie reuse from atypical devices, and access from TOR/VPN egress.
  • Hunt for stealer artifacts in endpoints and outbound traffic (e.g., suspicious ZIP/RAR exfil to Telegram).
  • Educate users on malvertising and fake installers
  • Make “type the URL” and “no downloads from ads” part of your culture.
  • Use Attack Surface Reduction (ASR) and script controls
  • Microsoft’s ASR rules can block credential theft and common dropper behaviors (Microsoft Defender guidance).
  • Segment and least-privilege
  • Don’t let a compromised workstation bridge into crown jewels. Scope local admin narrowly.

Here’s why this works: infostealers thrive on convenience—yours. When you break their shortcuts (malvertising clicks, saved passwords everywhere, long-lived sessions), you make yourself a terrible target.

What To Do If You Think You’re Infected

Speed matters. The sooner you act, the less damage attackers can do.

  1. Disconnect from the network – If it’s a laptop, disable Wi-Fi. Don’t keep browsing “to check one more thing.”
  2. Move to a clean device for account recovery – Don’t reset passwords on a possibly infected machine.
  3. Change passwords for critical accounts – Start with email, financial, cloud storage, and work SSO. Use unique, strong passwords.
  4. Sign out of all sessions – From each account’s security settings, sign out everywhere. Revoke unfamiliar OAuth apps.
  5. Turn on (or upgrade) MFA – Prefer security keys or passkeys if supported.
  6. Scan and remediate – Run a reputable antivirus/EDR scan. If malware is confirmed, consider a full OS reinstall.
  7. Watch finances and consider a credit freeze – Alert your bank. Add transaction alerts. Consider freezing credit as advised by the FTC.
  8. Notify your workplace if you used your device for work – They may need to revoke tokens, audit access, and rotate secrets.

If cryptocurrency wallets or keys were present on the device, assume compromise and move assets to new wallets with new seed phrases from a clean device.

Common Myths About Infostealers, Debunked

  • “MFA makes me bulletproof.” Helpful, not bulletproof. Stolen cookies can bypass MFA until you force reauth.
  • “Macs don’t get info-stealing malware.” They do. AMOS is a macOS-focused stealer (Kaspersky).
  • “I’ll know if I’m infected.” Not always. Stealers are designed for stealth and speed.
  • “I only browse safe sites.” Malvertising can put malicious installers on the very first page of search results (Microsoft).

Action Plan: A 15-Minute Hardening Sprint

If you do nothing else today: – Turn on MFA for email, banking, and your password manager. – Export weak/reused passwords and replace them with unique ones. – Delete saved cards from your browser; add them only in a dedicated payment app if needed. – Create two browser profiles: “Sensitive” and “Everything Else.” – Audit your downloads folder. Delete unknown installers. Uninstall shady apps. – Bookmark official vendor pages for the apps you use.

It’s simple, but it cuts out most of the easy wins for attackers.

Sources and Further Reading

FAQs About Infostealers

Q: What is an infostealer? A: It’s malware designed to grab sensitive data—passwords, cookies, payment info, crypto wallets—from your device and send it to attackers. They’re often delivered through malicious ads, fake installers, or cracked software.

Q: How do infostealers get on my computer? A: The most common paths are malvertising (fake sponsored results), phishing, and pirated software. Attackers also use fake updates and trojanized installers hosted on lookalike domains.

Q: Can antivirus detect infostealers? A: Often, yes—especially after a campaign becomes widespread. But there’s always a lag. Defense-in-depth (safe downloads, MFA, separate browser profiles) reduces reliance on detection alone.

Q: Are browser-saved passwords safe to use? A: They’re convenient, but they’re a high‑value target for stealers. A dedicated password manager with strong MFA and security keys is a safer bet.

Q: What is session hijacking, and can MFA stop it? A: Session hijacking uses your stolen session cookie to impersonate you. Many MFA setups won’t trigger during a cookie replay. That’s why signing out of all sessions and forcing reauth is key after a suspected infection.

Q: How long do stolen cookies stay valid? A: It varies by site. Some expire quickly; others last weeks or months. That’s why attackers love them. Organizations can mitigate this by shortening session lifetimes and binding tokens to devices.

Q: What should I do if I clicked a malicious ad or installed a fake app? A: Disconnect from the internet, use a clean device to reset passwords and sign out of all sessions, enable MFA, and scan the original device. If you used it for work, notify your IT team.

Q: Do passkeys and security keys help? A: Yes. They’re phishing-resistant and cut off many credential theft paths. They don’t magically fix cookie theft, but they reduce the chances of initial account compromise.

Q: Is macOS safe from infostealers? A: No platform is immune. Mac-focused stealers like AMOS actively target Safari keychain items and crypto wallets.

Q: Can I see if my data was sold on the dark web? A: There’s no perfect visibility. Services like Have I Been Pwned can alert you to known email breaches, and some security firms monitor stealer log shops for corporate domains. But prevention is far more reliable than detection after the fact.

The Bottom Line

Infostealers are effective because they exploit habits we’ve learned to love—saving passwords, staying logged in, and trusting what looks familiar in search results. The fix isn’t fear; it’s small, decisive upgrades to how you browse and authenticate.

If you do one thing today, lock down your most important accounts with security keys or passkeys, move your passwords into a real password manager, and stop downloading software from ads. The rest becomes much easier.

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InnoVirtuoso

Hello there! I'm passionate content writer navigating the digital landscape. With a deep love for words and an insatiable curiosity about technology.

With 10 years of experience in IT field, I write mostly about emerging tech, sharing news, informational articles and covering other topics I find interesting.

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