What Are Infostealers?

Last updated: 24 November 2025

Infostealers are a type of malware designed to silently collect and exfiltrate sensitive data such as passwords, cookies, tokens and autofill details. They have become one of the most common sources of credential exposure worldwide and play a major role in account takeover (ATO), fraud, and larger security incidents.

This article explains what infostealers are, how they work, and how Selki helps you detect and respond to these threats.

1. Overview

Infostealers (also called information stealers) operate quietly and focus on harvesting identity-related information from infected devices. They do not encrypt data or damage files; instead, they steal access.

In 2025, infostealers are responsible for a significant portion of the leaked credentials circulating in underground markets and criminal forums.

2. Why Infostealers Matter in 2025

Recent threat intelligence shows:

• Over 1.8 billion credentials were identified in 2025 stemming from infostealer infections.
• Malware-as-a-service (MaaS) models allow criminals to rent infostealers for US$100–300/month.
• Many major breaches start with stolen credentials rather than infrastructure intrusions.
• macOS is now heavily targeted by modern stealer families, expanding the attack surface.
• Large combined leaks (hundreds of millions of records) are becoming more frequent.

Infostealers are now one of the fastest-growing identity threats globally.

3. How Infostealers Work

A. Distribution

Infostealers often spread through:

• Phishing emails
• Fake installers, cracked software or trojanized apps
• Malicious ads (malvertising)
• Drive-by downloads
• Exploitation of outdated software

B. Data Collection

Once executed, they can extract:

• Saved passwords from browsers
• Session cookies and authentication tokens
• Autofill data
• Clipboard contents
• Crypto wallet keys
• VPN/RDP credentials
• System fingerprints

Most infostealers run for a few seconds, exfiltrate data and self-terminate.

C. Exfiltration

Stolen data is typically:

• Uploaded to attacker servers
• Sold in bulk on underground marketplaces
• Shared through leak channels
• Used for account takeover and fraud

4. Why They Are Dangerous

• Stealth: infections often go unnoticed.
• MFA bypass: session cookies allow login without passwords.
• Credential reuse risk: one password may open multiple systems.
• High-value targets: attackers frequently prioritize SaaS, fintech, marketplaces and portals.
• Foundation for larger attacks: BEC, fraud, ransomware and internal compromise often begin with infostealer data.

5. Common Infostealer Families

Examples include:

• RedLine
• Raccoon
• Lumma
• Vidar
• RisePro
• Atomic Stealer (AMOS, macOS)
• MetaStealer (macOS)

6. How Selki Helps

Selki is designed to detect credential exposures caused by infostealer infections affecting your employees, users or customers.

A. Continuous Monitoring

Selki monitors billions of leaked credentials across multiple intelligence sources and alerts you when:

• Credentials tied to your domain appear in stealer logs
• High-risk accounts are exposed
• Administrative or privileged access credentials appear in leaks
• User accounts show signs of compromise

B. Deep Visibility

In the Selki dashboard, you can see:

• Exposed username/email
• Metadata from the leak source
• Exposure classification (infostealer, breach, forum, paste)
• Severity level
• Recommended response actions

C. Early Warning

Because stealer logs often appear before incidents escalate, Selki acts as an early detection layer against:

• Account takeover attempts
• Credential stuffing
• Internal account compromise
• Supply chain/partner exposure

D. Designed for High-Volume Authentication Platforms

Selki is ideal for companies with large user bases (SaaS, fintech, marketplaces, B2B2C/B2C) where compromised credentials present systemic risk.

7. Prevention Best Practices

Technical Controls

• Enforce MFA or passkeys
• Require strong, unique passwords
• Deploy EDR with behavioral detection
• Patch systems regularly
• Monitor abnormal login behavior
• Apply least-privilege access

Organizational Controls

• Provide phishing awareness training
• Audit for shared or reused credentials
• Use password managers internally
• Rotate credentials after incidents
• Maintain an incident response plan for identity compromise

End-User Recommendations

• Avoid cracked/pirated software
• Enable MFA everywhere
• Keep systems updated
• Reset passwords after any suspicious activity
• Avoid storing sensitive credentials in browsers

8. Summary

Infostealers are one of the most impactful threats today due to their ability to steal credentials silently and enable larger cyberattacks. Selki helps protect your organization by monitoring leaked credentials, detecting exposures early, and providing actionable visibility for fast response.

For assistance, contact support@selki.io.

Updated on: 24/11/2025