What Are Infostealers? Understanding One of Today’s Most Dangerous Malware Threats
Introduction
In modern cybercrime, data has become the primary currency. Credentials, session cookies, personal identities, and internal access keys now trade at scale across underground markets. At the center of this ecosystem sits a powerful and fast-growing class of malware. Understanding what are infostealers is essential for organisations that want to prevent breaches before attackers ever touch their networks.
Infostealers operate silently, extracting sensitive information from infected devices and delivering it directly to cybercriminals. Unlike ransomware or destructive malware, their goal is not disruption — it is intelligence. That intelligence fuels fraud, account takeover, espionage, and large-scale cybercrime. At Munit.io, we see how stolen credentials and data harvested by infostealers are often the first step in a much larger attack chain.
What Are Infostealers?
To explain what are infostealers, they are a category of malicious software designed to secretly collect data from infected systems and send it back to an attacker. They typically target:
- Login credentials
- Browser cookies and session tokens
- Autofill data
- Crypto wallets
- Email and VPN credentials
- Files and screenshots
- System and network information
Infostealers often run quietly in the background, leaving few visible traces. Victims may never realise their device has been compromised — yet their digital identity may already be circulating in criminal markets.
How Infostealers Work
Understanding what are infostealers requires examining their operational flow.
1. Initial Infection
Infostealers commonly spread through:
- Phishing emails
- Malicious downloads
- Fake software installers
- Cracked or pirated software
- Malvertising and drive-by downloads
The user unknowingly installs the malware, giving it access to the system.
2. Data Collection
Once active, the infostealer scans the device for stored credentials, browser data, crypto wallets, and files. Modern variants can also grab session cookies that bypass multi-factor authentication.
3. Exfiltration
Collected data is compressed and sent to a command-and-control server or directly to the attacker.
4. Monetisation
The stolen data is packaged into logs and sold, traded, or used to conduct further attacks.
This pipeline explains why infostealers are such a powerful foundation for modern cybercrime.
Why Infostealers Matter to Businesses
Understanding what are infostealers is not just a technical concern — it is a strategic risk.
Credentials Become Attack Vectors
Once stolen, credentials allow attackers to log into cloud services, VPNs, email systems, and internal applications without triggering alarms.
Breaches Start Before the Breach
Infostealers enable criminals to map environments, identify valuable targets, and prepare attacks long before defenders detect anything.
Third-Party Risk
Employees, vendors, and partners can all be compromised, creating indirect entry points into corporate systems.
Long-Term Exposure
Stolen data can circulate for months or years, making past infections a present-day threat.
This makes infostealers one of the most important malware families to monitor externally.
Common Types of Infostealers
Credential Stealers
Designed to harvest usernames and passwords from browsers, email clients, and applications.
Cookie and Session Grabbers
These bypass security controls by hijacking active login sessions, even when MFA is enabled.
Crypto Stealers
Target digital wallets and seed phrases to enable direct financial theft.
Screenshot and Keylogging Tools
Capture user activity, giving attackers insight into workflows and sensitive operations.
Each type contributes to a complete profile of the victim.
Threats and Consequences
Understanding what are infostealers becomes urgent when examining the damage they enable.
- Account takeover and fraud
- Business email compromise
- Cloud environment breaches
- Data leaks and regulatory exposure
- Ransomware deployment
- Supply-chain compromise
Infostealers are rarely the final attack — they are the gateway.
Security authorities such as CISA consistently warn that infostealers play a key role in enabling ransomware attacks, fraud, and large-scale data breaches.
Use Cases: How Infostealers Enable Real Attacks
Case 1 – Cloud Account Compromise
An employee’s personal device was infected by an infostealer. Cloud credentials stored in the browser allowed attackers to access corporate storage and exfiltrate sensitive files.
Case 2 – Financial Fraud
Session cookies stolen from a finance employee’s browser enabled attackers to bypass MFA and initiate fraudulent transactions.
Case 3 – Ransomware Preparation
Attackers used infostealer logs to map network access, then returned weeks later to deploy ransomware with precision.
Each example shows how small infections lead to enterprise-level incidents.
Comparison: Infostealers vs Ransomware
| Feature | Infostealers | Ransomware |
|---|---|---|
| Visibility | Low | High |
| Objective | Data theft | Disruption & extortion |
| Detection | Often delayed | Immediate |
| Impact | Long-term | Acute |
| Use in Attack Chain | Early stage | Late stage |
Infostealers quietly shape the battlefield long before ransomware appears.
Best Practices to Defend Against Infostealers
To reduce risk, organisations must address both technical and external exposure.
Strengthen Endpoint Hygiene
Regular patching, modern endpoint protection, and application controls reduce infection risk.
Enforce Credential Security
Use MFA, avoid storing passwords in browsers, and limit session persistence.
Educate Employees
Many infections start with phishing or fake downloads.
Monitor External Exposure
The most important step is knowing when credentials and data are already in circulation.
This is where SAGA® by Munit.io plays a critical role. By continuously monitoring the surface, deep, and dark web for exposed credentials, infostealer logs, and identity leaks, SAGA allows organisations to detect compromise early — often before attackers use the data.
Why External Visibility Matters
Understanding what are infostealers also means recognising that most of their impact occurs outside your perimeter. Your security tools may never see the malware — but the stolen data appears in criminal marketplaces, underground channels, and breach collections.
External intelligence transforms that hidden activity into actionable insight.
Conclusion
So, what are infostealers? They are silent data-harvesting engines that power today’s most damaging cyberattacks. By stealing credentials, sessions, and personal information, they give criminals the keys they need to move undetected through digital environments.
Organisations that rely only on internal security miss where the real damage begins. With external visibility, rapid detection, and proactive response, infostealer-driven attacks can be stopped before they escalate.
Take control of your exposure — request a SAGA® demo and see compromised identities before attackers use them.