Infostealer malware is spyware that silently extracts browser passwords, session cookies, autofill data, and cryptocurrency wallet files by injecting malicious code directly into running browser processes. As of 2025, infostealers had stolen 1.8 billion credentials from 5.8 million infected devices, representing an 800% surge, with the average infected device leaking 44 credentials and 1,861 cookies, according to Flashpoint and DeepStrike.
Unlike ransomware or destructive malware, infostealers operate silently and at scale through criminal-as-a-service subscriptions. Attackers resell stolen data and access to other criminals, amplifying harm across victim organizations and individuals. The threat has accelerated in 2026 with new variants like Storm adding remote decryption capabilities before exfiltration.
Table of Contents
- How Infostealers Extract Your Data
- The Current Infostealer Landscape
- Why Session Cookies Bypass Multi-Factor Authentication
- Cryptocurrency and High-Value Assets
- Detection and Evasion Challenges
- Frequently Asked Questions
How Infostealers Extract Your Data
Infostealers inject code into running browser processes to harvest passwords, session cookies, authentication tokens, autofill data, and cryptocurrency wallet files, according to SentinelOne. Browsers store decrypted cookies in memory during active sessions—infostealers read this plaintext data directly and transmit it to attacker-controlled servers.
The malware also extracts cached autofill information and any cryptocurrency wallet files stored on the infected system. Cryptocurrency wallets pose a particular risk: stolen wallet files grant attackers direct access to cryptocurrency assets without requiring wallet passwords, as documented by Spyboy. This means a crypto holder's funds can be transferred immediately, regardless of password complexity or authentication method.
The Current Infostealer Landscape
The three dominant infostealer families—Lumma, StealC, and RedLine—account for over 75% of all infections and operate as malware-as-a-service subscriptions starting at $250 per month, according to GridinSoft. This low barrier to entry has democratized credential theft; attackers without advanced technical skills can purchase subscriptions and resell the stolen data.
As of September 2026, LummaC2, ACRStealer, StealC, and Vidar represent the most actively distributed infostealer families targeting credentials and wallets. A newer variant, Storm, emerged in 2026 with an additional capability: it remotely decrypts stolen credentials and browser data before sending results to attacker servers, according to Infosecurity Magazine. This removes a decryption step that previously required attackers to maintain their own infrastructure locally.
Why Session Cookies Bypass Multi-Factor Authentication
Session cookies stolen from active browser sessions are particularly dangerous because they allow attackers to bypass multi-factor authentication and impersonate users through replay attacks from another machine, according to Varonis. A stolen valid cookie from an authenticated session recreates the user's logged-in state on attacker systems without requiring the original password or triggering MFA prompts.
The duration problem compounds the risk: stolen cookies often remain valid longer than typical password-reset timelines. This gives attackers an extended window to access email accounts, banking platforms, cryptocurrency exchanges, and corporate systems while the victim remains unaware. Password resets provide no protection against active session hijacking because the attacker already possesses a valid session token.
Cryptocurrency and High-Value Assets
Infostealers target cryptocurrency wallets because wallet files are often stored unencrypted or encrypted with weak passwords on the same device where browsers run. Once a wallet file is extracted, attackers gain direct access to the cryptocurrency without needing the wallet password.
This applies to desktop wallets, exchange credentials stored in browsers, and any cryptocurrency holdings accessible through the compromised device. The financial speed of blockchain transfers means stolen crypto can be liquidated or moved through mixers within minutes, making recovery nearly impossible.
Detection and Evasion Challenges
Infostealers use the same legitimate Windows APIs that browsers employ daily, making their activity blend into normal process behavior and evade detection, according to Huntress. Browser process injection appears as routine functionality to security tools that rely on behavioral signatures.
Traditional endpoint detection struggles because the malware leaves minimal disk artifacts and operates entirely in memory during active sessions. This design choice explains why infostealer campaigns have scaled so dramatically—defenders cannot easily distinguish legitimate browser data collection from malicious extraction.
Frequently Asked Questions
Can I protect my crypto wallet if my computer is infected with infostealer malware?
If an infostealer has extracted your wallet file, the malware already has access to your cryptocurrency regardless of password strength. Prevention (not running untrusted files and maintaining updated security software) is far more effective than recovery. Moving cryptocurrency to a hardware wallet disconnected from internet-connected devices is the only reliable protection if you suspect prior infection.
Does multi-factor authentication stop attackers who steal my session cookies?
No. A stolen session cookie from an authenticated browser session recreates your logged-in state without triggering MFA, since MFA only protects the login step itself. Session hijacking bypasses MFA entirely, which is why stolen cookies are especially dangerous.
How does an infostealer get onto my computer in the first place?
The verified research provided focuses on what infostealers steal and how they operate, not infection vectors. Infostealers typically arrive through common malware delivery methods like malicious email attachments, compromised websites, or cracked software downloads.
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