What Is an Infostealer? How Credential-Stealing Malware Works in 2026

An infostealer is a type of malware specifically designed to extract sensitive data from infected devices, including saved passwords, browser cookies, session tokens, and cryptocurrency wallets. Unlike ransomware, infostealers operate silently, exfiltrating credentials in seconds before the victim even realizes they have been compromised. They represent one of the fastest-growing threats in cybersecurity today.

How does an infostealer work?

Infostealers follow a precise attack chain that makes them devastatingly efficient. Once delivered to a victim’s machine, typically through phishing emails, malicious ads, or cracked software downloads, the malware executes within seconds and begins harvesting data from predictable locations on the operating system.

The attack unfolds in four stages. First, the initial infection occurs when a user downloads a trojanized file or clicks a malicious link. Second, the stealer scans the device for valuable data targets, including browser password stores, autofill databases, cookie jars, and cryptocurrency wallet files. Third, all harvested data is packaged into a structured “log” file and exfiltrated to a command-and-control server. Fourth, the stolen credentials are sold on dark web marketplaces, shared in Telegram channels, or compiled into combo lists for credential stuffing attacks.

According to the IBM X-Force Threat Intelligence Index 2024, infostealer-related activity increased by 266% year-over-year, making it the most rapidly growing category of malware observed in the wild. The speed of the attack is what makes infostealers particularly dangerous: the entire process, from infection to exfiltration, takes less than 30 seconds in most cases.

What data does an infostealer steal?

The scope of data that modern infostealers target is broader than most organizations realize. A single successful infection can compromise an employee’s entire digital identity and, by extension, every corporate system they have access to.

Infostealers typically harvest saved passwords from all installed browsers (Chrome, Firefox, Edge, Opera), active session cookies that allow attackers to bypass multi-factor authentication entirely, autofill data including credit card numbers and personal addresses, cryptocurrency wallet files and seed phrases, VPN and RDP credentials, FTP and SSH keys, desktop application tokens for Slack, Discord, and Telegram, and system information including hardware IDs, IP addresses, and installed software. The Verizon Data Breach Investigations Report 2024 found that stolen credentials were involved in 31% of all breaches over the past decade, confirming that credential theft remains the most reliable initial access vector for attackers.

What are the major infostealer families?

The infostealer ecosystem is dominated by several malware families, each sold as a service (Malware-as-a-Service) to cybercriminals on underground forums. Understanding these families helps security teams recognize the threat landscape they face.

RedLine Stealer

RedLine has been one of the most widely deployed infostealers since its emergence in 2020. Sold on underground forums for as little as $150 per month, it targets browser data, cryptocurrency wallets, and system information. Despite law enforcement disruptions, variants continue to circulate. RedLine logs make up a significant portion of the stolen credential market.

Raccoon Stealer

Raccoon Stealer operates on a subscription model and is known for its ease of use, making it accessible even to low-skill attackers. Version 2.0, rebuilt from scratch in C/C++, introduced improved evasion techniques and faster exfiltration. It targets a wide range of applications and browsers.

Vidar Stealer

Vidar is a fork of the older Arkei stealer, specialized in harvesting browser data, two-factor authentication software databases, and cryptocurrency wallets. It uses legitimate infrastructure like Mastodon and Steam profiles to retrieve its command-and-control server addresses, making it harder to block through traditional network filtering.

LummaC2

LummaC2 represents the newest generation of infostealers, with advanced anti-analysis capabilities and a sophisticated distribution network. According to threat intelligence reports, LummaC2 has rapidly gained market share since 2023, using techniques such as fake CAPTCHA pages and malicious GitHub repositories to distribute itself. Its logs are increasingly prevalent in dark web marketplaces and Telegram channels.

How are stolen credentials distributed?

Once an infostealer exfiltrates data, the stolen credentials enter a well-organized underground economy. Attackers sell individual logs on marketplaces like Russian Market or Genesis Market, where buyers can search for credentials by domain, country, or application type.

Bulk credential data is also compiled into combo lists, massive text files containing millions of username-password pairs, which are then used for automated credential stuffing attacks. Telegram has become a primary distribution channel, with private and semi-private channels sharing fresh logs daily. Stealed monitors over 100 million new credentials per day from these sources, providing organizations with real-time visibility into leaked credentials that traditional security tools miss entirely.

How can you protect against infostealers?

Defending against infostealers requires a layered approach that addresses both prevention and detection. No single measure is sufficient on its own.

For prevention, organizations should enforce endpoint detection and response (EDR) solutions across all devices, disable browser password saving in favor of enterprise password managers, implement application whitelisting to prevent unauthorized executables, train employees to recognize phishing attempts and avoid downloading cracked software, and enforce the principle of least privilege so that a single compromised account limits blast radius.

For detection, the critical gap is knowing when credentials have already been stolen. Traditional security tools focus on preventing infection, but they cannot tell you that an employee’s credentials appeared in a stealer log posted to a Telegram channel two hours ago. This is where credential leak monitoring becomes essential.

How does Stealed detect infostealer compromises?

Stealed fills the detection gap by continuously monitoring the sources where stolen credentials actually appear: infostealer log marketplaces, dark web forums, combo lists, and private Telegram channels. When credentials matching your organization’s domains are detected, you receive real-time alerts through Slack, Microsoft Teams, or webhooks.

Unlike services that rely on breach databases published after the fact, Stealed ingests and analyzes raw stealer logs as they are distributed. This means you can detect compromised credentials within hours of exfiltration, not weeks or months later. Each alert includes contextual information such as the stealer family that harvested the data, the infected machine’s details, and the full scope of exposed credentials.

The platform processes over 100 million credentials daily, making it possible to detect threats at a scale that manual monitoring simply cannot achieve. Security teams can then take immediate action, forcing password resets, revoking sessions, and investigating the scope of compromise before attackers have a chance to exploit the stolen access.