Glossary
What is infostealer?
An infostealer is a class of malware that silently harvests credentials from an infected device — saved browser passwords, session cookies, autofill data, crypto wallets — and ships them to the attacker. The harvested output, sold in bulk as 'logs' on criminal markets for a few dollars, has become one of the most common raw materials for ransomware and account-takeover attacks.
Why infostealers matter for security
Infostealers turn a single careless download — a cracked app, a fake installer, a malicious ad — into a complete copy of everything a browser knows: corporate logins, VPN credentials, email sessions, cloud consoles. Unlike ransomware, the infection is quiet; many victims never know it happened.
The stolen data is packaged into 'logs' and sold on dark web markets and Telegram channels. Ransomware affiliates and initial-access brokers buy these logs in bulk, test the corporate credentials inside, and use whatever still works as their way in. In HookPhish's H1 2026 ransomware analysis, 58% of leak-site victims had employee or customer credentials already circulating in infostealer logs at the time the victim record was compiled.
Infostealer vs. keylogger
A keylogger records what a user types going forward. An infostealer is faster and greedier: it raids what is already stored — password vaults, cookies, tokens — in seconds, then often deletes itself. A session cookie stolen this way can even bypass MFA, because the attacker replays an already-authenticated session.
How to prevent infostealer
- Monitor criminal markets for your organization's credentials in infostealer logs.
- Ban personal-device access to corporate apps without device controls.
- Enforce MFA and short session lifetimes so stolen cookies and passwords age out fast.
- Train employees to spot the fake installers, cracked software and malvertising that deliver stealers.
- Force password resets the moment an exposure is detected.
How HookPhish helps
HookPhish's dark web and breach monitoring watches infostealer logs and criminal markets for your organization's exposed credentials and alerts you — with guided response — before an attacker puts them to work.
Frequently asked questions
How do infostealers spread?+
Mostly through fake or 'cracked' software downloads, malicious ads, phishing attachments and compromised browser extensions. The infection typically takes seconds and leaves little visible trace.
What is an infostealer 'log'?+
The packaged output of one infected device: saved passwords, cookies, autofill data, system details and screenshots. Logs are sold in bulk on dark web markets and messaging channels, often for only a few dollars each.
Can infostealers bypass MFA?+
Indirectly, yes. Stolen session cookies let attackers replay an already-authenticated session without ever seeing a password or MFA prompt — which is why short session lifetimes and re-authentication for sensitive actions matter.
How do infostealers relate to ransomware?+
Stolen credentials are a primary initial-access route for ransomware crews. Affiliates and access brokers buy infostealer logs, test the corporate logins inside, and resell or use working access to deploy ransomware.
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