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 article explains what infostealer malware is, how it affects businesses and what organizations can do to reduce their exposure.
What Infostealer Malware Is and How It Gets In
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 allow days or weeks to pass 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.
What Attackers Do With Stolen Credentials
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.
How Infostealers Bypass MFA
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. A session token is a temporary credential issued after a user successfully logs in, including after completing an MFA prompt, that tells the application to keep the user authenticated without requiring them to verify again.
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.
How Infostealer Attacks Affect Businesses
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.
Risk Mitigation Strategies
Organizations can reduce the risk of infostealer attacks with the following strategies:
Use MFA on all business accounts. MFA is a necessary control and should be in place across all business applications. Since it can be bypassed through session token theft if a device is compromised, MFA works best as part of a broader security approach rather than a standalone solution. Phishing-resistant forms of MFA, such as hardware security keys or passkeys, offer stronger protection than SMS-based verification.
Limit access to what employees need. Applying the principle of least privilege means employees can only access the systems and data required for their role, which reduces the potential damage from any single compromised account.
Keep software and systems updated. Some infostealers exploit known vulnerabilities in outdated software, while many others rely on phishing or malicious downloads. Applying updates promptly and using patch management tools can help close these gaps.
Deploy endpoint protection on all devices. Endpoint detection and response tools can identify infostealer behavior and flag suspicious activity. This protection should extend to personal devices used for work, not just company-issued equipment.
Train employees to recognize phishing. Phishing emails remain the most common delivery method for infostealer malware. Regular security awareness training that covers how to identify suspicious emails and links reduces the likelihood of a successful infection.
Respond quickly to detected compromises. If a credential is known or suspected to be compromised, treat it as an immediate security event. Resetting credentials and investigating scope promptly can interrupt the attack chain before it escalates.
Maintain cyber insurance as a financial backstop. If an infostealer infection leads to a ransomware attack, data breach or business interruption, a cyber policy may help cover response costs, notification expenses and lost income. Coverage will depend on the policy language, the security controls in place at the time of the incident and the nature of the resulting loss.
Conclusion
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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This Cyber Risks & Liabilities document is not intended to be exhaustive nor should any discussion or opinions be construed as legal advice. Readers should contact legal counsel or an insurance professional for appropriate advice. © 2026 Zywave, Inc. All rights reserved.
