When a cyberattack makes headlines, it is usually because of ransomware, a large data breach or a fraudulent wire transfer. What is less visible is often what made the attack possible in the first place: A stolen password. Infostealer malware is designed specifically to collect login credentials and other sensitive data from infected devices and send that information to the attacker, often without the victim ever noticing.
This post explains what infostealer malware is, how it affects businesses, and what organizations can do to reduce their exposure to it.
Infostealer malware is designed to collect login credentials, saved passwords, session tokens, and other sensitive data from a compromised device and transmit that information to the attacker. Session tokens are small files that keep a user logged in to an application, so stealing one can give an attacker access to an account without needing a password. Modern infostealers frequently target browser-stored passwords and authentication cookies.
Once installed, the malware runs quietly in the background with no obvious sign that anything is wrong. Attackers frequently wait days or weeks before using stolen credentials, which means a business may not connect an infection to a later breach.
Common ways infostealers reach business devices include phishing emails containing malicious links or attachments, fake software updates or downloads from compromised websites, malicious files disguised as legitimate software, and personal devices used for work that lack adequate endpoint protection.
Stolen credentials are frequently sold on criminal marketplaces, where other threat actors purchase them and use the access to log in to business systems as a legitimate user. Valid credentials allow attackers to bypass many security controls without triggering obvious alerts.
A single set of stolen credentials can open access to email, file storage, accounting software, and other connected applications simultaneously, particularly in organizations that rely heavily on cloud-based tools. Attackers who gain this kind of access can move through a network, escalate their privileges, and deploy ransomware or extract data for extortion.
Multifactor authentication (MFA) is one of the most widely recommended defenses against unauthorized account access, but infostealers can undermine it in a way many businesses do not anticipate. In addition to stealing passwords, infostealers can harvest session tokens from a compromised device.
When an attacker obtains a valid session token, they can inherit the user's authenticated session without repeating the MFA challenge. From the application's perspective, the request looks identical to one from the legitimate user. This technique, often called session hijacking or cookie theft, means that even an employee who follows MFA best practices can have their account compromised if their device is infected. Businesses that rely solely on MFA without also deploying endpoint protection and monitoring for suspicious login activity remain exposed even if every employee uses it consistently.
What makes infostealer infections particularly difficult to manage is the delay between compromise and consequence. Because the malware operates silently and stolen credentials may sit in criminal marketplaces for weeks before being used, businesses often have no indication that anything is wrong until an attacker is already inside their systems. An attacker with valid credentials and time to move through a network is better positioned to launch ransomware, extract sensitive data, or initiate fraudulent transactions than one who triggers alerts at the point of entry.
That delayed visibility also complicates the response. Regulatory notification obligations, legal exposure, and reputational damage do not wait for a business to fully understand what happened. Infostealers are opportunistic, and any compromised device is a potential entry point regardless of company size.
Organizations can reduce the risk of infostealer attacks with the following strategies:
Infostealer malware is effective because it draws no attention. By the time a business realizes something is wrong, the stolen credentials may already be in use. Proactive controls are critical because once an attacker has valid credentials and time inside a network, containment becomes far more difficult. MFA, access management, endpoint protection, and employee training each address a different part of the exposure, and the strength of that combination is what makes it difficult for an attacker to convert a stolen credential into a serious incident.
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The above information does not constitute advice. Always contact your insurance broker or trusted advisor for insurance-related questions.