Summary: Infostealer malware steals sensitive data, such as login credentials or banking details, from devices, leading to data breaches, financial loss, and unauthorized access.
Infostealer malware is a major cybersecurity risk. This threat can bypass the security features in a standard browser, leaving your business vulnerable to attacks. Relying solely on built-in browser security is not enough to prevent data breaches, financial loss, or reputational damage.
Recent industry data confirms the growing danger. IBM's 2025 X-Force Threat Intelligence Index reports a significant surge in this tactic, with an 84% increase in emails delivering infostealer malware. The report also highlights that 30% of intrusions now involve using valid credentials.
Understanding how infostealers work is the first step toward effective protection. Let’s look at how they operate and what you can do to prevent an attack.
Infostealer malware is a type of malicious software designed to steal sensitive information from infected devices. Cybercriminals, particularly initial access brokers (IABs), use it to collect passwords, banking details, personal files, and other private data, which they can sell to other threat actors, use for fraud, or exploit in further attacks.
Once deployed, the infostealer malware communicates with a command and control (C2) server, which allows attackers to exfiltrate data stolen from the compromised device and issue further commands. IABs often leverage infostealers to gain unauthorized entry into corporate networks, then either provide the stolen data to ransomware groups or sell access to other cybercriminals.
Initial access brokers spread infostealer malware through phishing emails, fake downloads, or malicious websites. Some advanced versions can even adapt their tactics based on the system they infect, making them harder to detect. Because they operate so quietly, infostealers pose a serious risk. A single infection can lead to identity theft, financial loss, or unauthorized access to critical systems.
Infostealer malware has been around for nearly two decades, evolving alongside the internet and online threats. It emerged in 2007 with Zeus (also called Zbot), a powerful Trojan designed to steal online banking credentials. The malware became a massive threat. When its source code leaked in 2011, hackers swiftly copied and modified it, creating a wave of new infostealers.
By 2008, infostealers began targeting more than just banking information. Koobface, another early infostealer, targeted the login credentials of social media users on platforms like Facebook, Twitter, MySpace, and email services like Gmail. It spread by hijacking social media accounts and tricking users' friends or connections into clicking suspicious links.
Today, infostealers are more advanced and operate within a sophisticated malware-as-a-service (MaaS) ecosystem. Many modern botnets, which are large networks of infected computers, possess infostealing capabilities, even if their main purpose is different. These threats now go beyond stealing banking information and social media credentials, which puts both individuals and businesses at risk, making infostealers a critical concern for enterprise cybersecurity.
Once inside a device, infostealer malware gathers a wide range of information, including:
Infostealers target login information, such as emails and passwords, VPN credentials, and session cookies—small files that keep users logged in to websites and online services. Cybercriminals use session cookies to hijack personal and corporate accounts and gain unauthorized access to email, banking, social media, and other sensitive platforms, all without needing a password or two-factor authentication (2FA).
Infostealers don't just target browser-based credentials. They also steal data stored by applications directly on a user's device. Popular targets include platforms like Steam, Discord, and Telegram, which store login credentials, authentication tokens, and metadata in specific directories rather than session cookies. Attackers can extract details such as stored accounts, user settings, login history, and even metadata like the number of games owned on Steam.
Many users store financial information, such as credit card details, banking credentials, and cryptocurrency wallet data, in their browsers for convenience. Infostealers can extract this data and give hackers access to bank accounts, online payment services, and cryptocurrency wallets. Access to this information can lead to significant financial loss.
Personally identifiable information (PII), such as Social Security numbers and addresses, is often a key target for identity theft. Criminals use it to impersonate victims, apply for loans, open fraudulent accounts, or commit other crimes. Stolen PII is highly valuable, which is why cybercriminals often sell it in bulk on hacker forums, marketplaces, and encrypted messaging platforms.
Infostealers can collect unique browser details, known as fingerprints, including settings, installed browser extensions, and system configurations. Attackers use this data to mimic a victim's device, making their activities appear legitimate and helping them bypass security measures. Some cybercriminals use anti-detect browsers to replicate stolen browser fingerprints, which allows them to evade fraud detection and security checks.
Infostealers can gather details about your device, including information about its operating system and hardware. Attackers can use this data to identify vulnerabilities, making it easier for them to launch targeted attacks or exploit your system.
Even when you use private browsing, infostealers can still track your session data and search history. Hackers can use this information to profile you and then target you with tailored phishing scams or other malicious attacks.
Your personal files, such as documents, photos, and videos, are valuable not only to you but also to cybercriminals. Infostealers can steal these files and exploit them for blackmail, fraud, or identity theft.
If cybercriminals steal your File Transfer Protocol (FTP) credentials, they can gain access to your servers and take control of your website or network. They may steal or modify important files, upload malware, and disrupt your system.
Once an infostealer collects data, it compiles everything into a stealer log, a file containing a detailed record of the victim's sensitive information. This log captures a complete snapshot of the victim's device, including saved passwords, browsing history, session cookies, and system details.
Cybercriminals distribute these logs on underground forums, marketplaces, and encrypted messaging platforms. Other hackers then use them for credential stuffing, financial fraud, cryptocurrency theft, or large-scale corporate breaches.
We can break down how infostealer malware works into four stages:
The first stage is malware deployment. Initial access brokers distribute infostealer malware through:
Once malware is deployed, the next stage is data collection. Common methods attackers use to collect data include:
Once infostealer malware collects sensitive information, the next step is to transmit it to the attacker's server. This can be done through various methods, including:
Once cybercriminals export stolen data, they quickly transfer it to centralized marketplaces or decentralized platforms. Centralized marketplaces, often found on the dark web, allow cybercriminals to sell logs individually. However, criminals rarely use dark web forums for log-selling.
Decentralized platforms, such as peer-to-peer networks like Telegram, are more popular because they offer greater anonymity and make transactions harder to trace. On these platforms, logs are often sold in bulk.
Once attackers have the data, they can use it for various malicious purposes, such as:
Infostealer malware comes in many forms, with hundreds—possibly thousands—of different strains. Some are well-known and widely studied, while others are designed to target specific individuals, industries, or regions.
Malware strains often work alongside other types of malware to maximize damage. These other types of malware include:
Infostealer malware has evolved over the years, adapting to security defenses and targeting different types of data. Some of the most infamous infostealers include:
Infostealer malware is a major threat, often used to steal sensitive information. Cybercriminals, particularly initial access brokers, deploy it to infiltrate systems and then sell access to other malicious actors or send data to ransomware groups.
Once inside compromised systems, attackers can steal sensitive data, leading to financial loss, identity theft, and severe security breaches. For businesses, the consequences go beyond stolen credentials, potentially resulting in regulatory penalties, operational disruptions, and lasting reputational damage.
Dangers posed by the infostealer malware include:
Infostealers can target anyone, but businesses are among the most common victims. Recent infostealer malware statistics from SpyCloud's 2024 Malware & Ransomware Defense Report show a rise in attacks, proving that no industry is safe from these threats. Cybercriminals see businesses as high-value targets because they store lots of valuable information. A single breach can expose thousands of accounts, making organizations far more lucrative than individual victims.
Industries like finance, healthcare, e-commerce, and technology are frequent targets. Attackers steal banking credentials, medical records, and customer payment data, while technology firms are targeted for intellectual property and infrastructure access. Governments and defense organizations also face attacks aimed at espionage and classified data theft.
High-net-worth individuals, executives, and investors are frequently targeted due to their financial assets. Social media users and influencers are also at risk because stolen accounts can be used to spread scams or demand ransom. Gamers and cryptocurrency traders often fall victim to infostealers that steal gaming accounts, digital assets, and crypto wallet credentials.
Infostealer malware operates quickly and quietly, often on devices outside your direct control. Because traditional security alerts are rarely triggered, early detection relies on recognizing the subtle signals.
While infostealers are designed to avoid detection, they leave clear indicators if you know where to look.
Here are common signs that an infostealer has targeted your organization:
Individually, these signs may not confirm an infostealer infection. However, when viewed together, they paint a clear picture. Your security depends on connecting these signals before a minor incident becomes a major breach.
Protecting your organization from infostealers requires a layered defense that combines strong technical controls, employee awareness, and proactive monitoring. Here are the essential steps to take..
Many infostealers operate undetected for weeks or months. Early recognition of infection signs can stop an attack before it escalates.
A multi-layered security strategy significantly reduces the risk of infostealer malware.
Cybercriminals use stolen credentials and session cookies to gain unauthorized access to business accounts and bypass security measures.
Phishing emails and malicious downloads are the most common ways infostealers spread.
Outdated software contains vulnerabilities that infostealers exploit.
Many malware infections occur due to human error, such as clicking on malicious links, reusing passwords, or downloading malicious files.
Infostealer malware is a silent threat, stealing credentials and sensitive data before you even realize it. Contact the NordStellar team to get complete visibility over your cyber threats.
The most common signs are anomalies in user and system behavior, such as suspicious login patterns from new locations, phishing emails sent from legitimate internal accounts, and login attempts using old or disabled credentials.
Attackers usually target industries with high-value data, such as finance, healthcare, e-commerce, and technology. Threat actors seek payment information, patient records, and intellectual property from these sectors. Government and defense organizations are also frequent targets for espionage.
Stolen data is sold as "stealer logs" on underground platforms. While some individual logs are sold on dark web marketplaces, bulk sales typically happen on encrypted messaging apps like Telegram, which offer cybercriminals greater anonymity.
Joanna Krysińska
Senior Copywriter
A writer, tech enthusiast, dog walker, and amateur pastry chef, Joanna grew up in a family of engineers and mathematicians, so a techy mind is in her genes. She loves making complex tech topics less complex and digestible. She also has a keen interest in the mechanics of cybercrime.
