What Is Infostealer Malware and Why Is It So Dangerous?

Quick answer: Infostealers are malware that silently harvest credentials, browser data, cookies, and session tokens from infected computers. This stolen data is sold to ransomware gangs, who use it to break into organisations. It's the most common entry point for major breaches in 2026.

What Infostealers Steal

Browser data:

• Saved passwords (all of them)
• Browser cookies and sessions
• Autofill data
• Browser history
• Saved payment cards

Application credentials:

• VPN credentials
• Email passwords
• FTP clients
• Database tools
• Development environments

System information:

• Installed software
• Screenshots
• Clipboard contents
• Cryptocurrency wallets
• Documents

Session tokens:

• Active login sessions
• OAuth tokens
• API keys
• Authentication cookies

With browser cookies, attackers can hijack active sessions—bypassing MFA entirely.

How Infostealers Spread

Common infection vectors:

Malicious downloads:

• Cracked software
• Fake updates
• Malicious ads (malvertising)
• Fake software (legitimate-looking)

Phishing:

• Email attachments
• Malicious links
• Drive-by downloads

Social engineering:

• Fake job offers with "test assignments"
• Malicious browser extensions
• Compromised legitimate software

Supply chain:

• Infected software packages
• Compromised development tools

The Infostealer Economy

How the market works:

1. Infostealer operators infect thousands of computers
2. Logs (stolen data bundles) are sold on dark web
3. Buyers search logs for corporate credentials
4. Initial Access Brokers package and resell corporate access
5. Ransomware gangs buy access and attack

A single infected home computer can compromise an entire enterprise if the user has work credentials saved.

Why This Matters Now

Scale

• Millions of devices infected globally
• Billions of credentials available on criminal markets
• Industrial-scale credential harvesting

Sophistication

• Infostealers evade most antivirus
• Operate briefly then vanish
• Designed to avoid detection

Impact

• Primary entry point for ransomware
• Session hijacking bypasses MFA
• Enables impersonation attacks
• Hard to trace back to source

The MFA bypass problem

Session token theft beats MFA: User authenticates → MFA succeeds → session token created → infostealer steals token → attacker uses token → no MFA challenge

This is how attackers get into MFA-protected accounts.

Defending Against Infostealers

Prevent infection

• EDR everywhere (infostealers evade basic AV)
• Web filtering (block malicious downloads)
• Software control (prevent unauthorized installations)
• User training (avoid suspicious downloads)

Reduce impact of infection

• Don't save passwords in browsers (use password manager with master password)
• Conditional Access (tie sessions to devices)
• Token binding (prevent session hijacking)
• Short session lifetimes

Detect compromise

• Dark web monitoring (watch for your credentials)
• Unusual login patterns (stolen sessions often come from unusual locations)
• Credential monitoring services
• Security awareness (users report suspicious activity)

Respond quickly

• Immediate session revocation when compromise suspected
• Credential reset for affected users
• Investigation of affected device

Practical Steps

For your organisation:

1. Deploy EDR on all endpoints (not just AV)
2. Implement Conditional Access with device compliance
3. Monitor for impossible travel and risky sign-ins
4. Consider dark web credential monitoring
5. Train users on software download risks

For high-value accounts:

• Hardware security keys (FIDO2)
• Shorter session timeouts
• Device-bound credentials
• Extra monitoring

What We Implement

We protect against infostealers through:

• EDR/MDR detecting infostealer behaviour
• Conditional Access limiting session hijacking risk
• Dark web monitoring alerting on leaked credentials
• Web filtering blocking malicious downloads
• Security awareness teaching users to avoid infection

Infostealers are the first step in most major breaches. We block that step.

---

about infostealer protection.

---