Learn how to respond to malware incidents by remediating stolen credentials and session tokens, not just cleaning devices.
• Isolate infected systems immediately but preserve volatile memory data for forensics instead of powering off.
• Infostealers exfiltrate credentials and session tokens within seconds, often before your EDR can respond.
• Resetting passwords alone fails because session tokens let attackers bypass both passwords and MFA entirely.
• Monitor dark web sources to detect when stolen credentials surface on criminal marketplaces before attackers exploit them.
Traditional malware incident response is broken. Most playbooks focus on one thing: cleaning infected devices. That made sense a decade ago. Today, it’s a recipe for getting breached again within weeks.
Here’s the problem. Modern infostealers don’t just infect your machine. They grab credentials and session tokens in seconds. By the time your EDR catches anything, your data is already being sold on dark web marketplaces for $10-15 per account.
In 2024, infostealers accounted for 24% of all observed security incidents. That’s more than malicious scripts and traditional malware combined. And 90% of organizations that were breached had their credentials available for sale on dark web marketplaces before anyone knew about the infection.
This guide gives you a complete malware incident response playbook. One that goes beyond just wiping devices to actually protecting your organization from the stolen data that attackers will use against you.
Malware incident response is how your security team detects, contains, and recovers from a malware infection while minimizing damage to your organization.
Malware incident response is the coordinated process of identifying, containing, eradicating, and recovering from malware infections. It includes isolating infected systems, analyzing the malware’s behavior, remediating affected accounts, and implementing controls to prevent reinfection. Effective response extends beyond device cleanup to address stolen credentials and session tokens.
The traditional approach treats malware incidents as device problems. You find the infected machine, quarantine it, remove the malware, and restore from backup. Done.
That approach fails against modern threats because it ignores what the malware actually stole. When an infostealer grabs your employee’s corporate credentials and session cookies, cleaning their laptop doesn’t revoke the access those stolen tokens provide. Attackers can still walk right into your systems using the stolen authentication data.
In 2024, the top three infostealer families (StealC, Lumma, Redline) infected 4.3 million devices. Redline alone compromised 9.9 million hosts. Each infection potentially captured dozens of credentials and session tokens. That’s why your malware incident response has to address both the infected device and the stolen data.
An effective malware incident response plan must be identity-centric, not just device-centric. You need to remediate both the infected endpoint and the stolen authentication data.
Traditional incident response was designed for malware that stayed on your systems. Ransomware encrypts files. Trojans maintain persistence. Rootkits hide in the kernel.
Infostealers work differently. They’re designed to operate in seconds and grab everything valuable. By the time you detect anything suspicious, your data has already been exfiltrated.
But the stolen data lives on.
Infostealer malware is a category of malicious software designed to harvest sensitive information from infected devices, including saved passwords, browser cookies, session tokens, and autofill data. Unlike ransomware, infostealers operate silently and exfiltrate data to criminal marketplaces within seconds of infection.
Here’s what a typical infostealer grabs in under 60 seconds:
The April 2024 Snowflake breach demonstrated exactly how this plays out. Attackers used credentials stolen by at least six different infostealer families to compromise 165 Snowflake customer environments. The result? Hundreds of millions of records exposed from companies including AT&T and Ticketmaster.
The infected devices were probably cleaned months earlier. The stolen credentials remained valid.
A complete malware incident response plan needs seven phases. Each phase builds on the previous one, and skipping steps creates gaps that attackers will exploit.
You can’t respond effectively to an incident you haven’t prepared for. Preparation happens before any infection occurs.
Build your IR team. Assign clear roles and responsibilities:
Define escalation paths. Not every malware infection requires the same response. A single compromised workstation differs from a domain-wide attack.
Secure your backups. Verify that critical system backups exist and haven’t been compromised. Test restoration procedures regularly. Attackers increasingly target backup systems to prevent recovery.
Establish monitoring. Deploy infostealer channel monitoring to detect when employee credentials appear in criminal marketplaces. This gives you early warning that an infection occurred, often before internal detection.
When malware is detected, your first goal is understanding what you’re dealing with.
Isolate infected systems immediately. Disconnect from the network via EDR policy, domain controls, or physically unplugging the ethernet cable. Disable VPN and cloud application access. The goal is preventing lateral movement while you investigate.
Don’t power off the machine. This is critical. Modern forensics depends on volatile memory data that disappears when you shut down. Memory contains running processes, network connections, and encryption keys that you’ll lose if you power down.
Analyze the malware. Determine the malware family and understand its capabilities:
Identify what was stolen. For infostealers, this is the most important question. Assume browser passwords and session tokens were captured, and scope your credential remediation accordingly.
Find the initial entry point. Review logs to determine how the infection occurred. Common vectors include phishing emails with malicious attachments and drive-by downloads from compromised websites. Understanding the entry point helps you close the gap.
Once you understand the threat, focus on stopping the spread.
Close entry points. If the malware came through email, block the sender and hash the attachment. If it was a malicious website, block the domain at your firewall. If it exploited a vulnerability, patch immediately.
Hunt for additional infections. Use the indicators of compromise (IoCs) from your analysis to search across all systems:
Segment your network. If the infection is widespread, implement additional network segmentation to contain the damage. Isolate critical systems and sensitive data repositories.
Update endpoint protection. Push IoCs to your EDR and antivirus platforms. Configure alerts to trigger on any new detections.
Remove the malware from all affected systems.
Preserve forensic evidence. Before you clean anything, preserve what you might need later:
These artifacts may be critical for legal proceedings and insurance claims.
Remove the malware. Use your endpoint protection tools to quarantine and remove detected malware. For severe infections or advanced threats, consider rebuilding systems from scratch rather than attempting cleanup.
Verify removal. Run multiple scans. Check for persistence mechanisms. Monitor for any signs of remaining infection.
Now it’s time to get back online without leaving gaps attackers can exploit.
Restore from clean backups. Use backups taken before the infection occurred. Verify the backup integrity before restoration. Scan restored data for malware before bringing systems back online.
Rebuild when necessary. For systems where backup restoration isn’t possible or where you can’t confirm a clean state, rebuild from known-good images. This is more time-consuming but provides higher confidence that you’re starting from a clean slate.
Remediate vulnerabilities. Address any security gaps identified during the investigation. Patch the software or fix the configuration that let the malware in. Vulnerability remediation is just as important as malware removal in preventing reinfection.
This is where most incident response playbooks stop. And this is exactly where they fail.
Cleaning infected devices doesn’t revoke stolen credentials. If an infostealer captured your employee’s corporate password and session tokens, attackers can still use that data to access your systems.
Reset all potentially compromised passwords. Force password changes for every account that may have been exposed:
Make sure employees create new passwords from clean devices. Resetting a password from an infected machine just gives the attacker the new credential.
Invalidate active sessions. This step is critical and often overlooked. Session tokens allow attackers to bypass both passwords and MFA. A valid session cookie grants full access without any authentication challenge.
Contact application vendors or use administrative controls to:
Enforce MFA everywhere. If affected accounts didn’t have multi-factor authentication, implement it now. While MFA doesn’t stop session token theft, it does prevent credential-only attacks.
Monitor for credential abuse. Deploy ongoing dark web monitoring to detect when stolen credentials appear on criminal marketplaces. This provides early warning of potential account takeover attempts before attackers can act on the stolen data.
Every incident is an opportunity to improve.
Conduct a post-incident review. Gather your incident response team and walk through:
Update procedures. Modify your incident response playbook based on lessons learned. Document new IoCs, attack patterns, and response procedures.
Strengthen defenses. Implement controls to prevent similar incidents:
Create documentation. Write up what happened for your security team and a shorter version for leadership. Cover the timeline, what was impacted, and what you’re doing to prevent it from happening again.
Infostealer incidents require special consideration because the attack doesn’t end when you clean the device.
In 2024, infostealers fueled a 33% increase in stolen credentials compared to the previous year. Over 200 million credentials were stolen in just the first two months of 2025. These numbers represent ongoing risk for every organization whose employees were infected.
Verizon’s 2025 Data Breach Investigations Report found that 30% of compromised systems were enterprise-sponsored devices. Even more concerning, 46% of infostealer infections occurred on non-managed personal devices that also contained business credentials. BYOD policies create significant exposure.
When responding to a suspected infostealer infection:
Assume broad credential exposure. Infostealers don’t just grab one password. They harvest everything accessible on the system, including passwords typed into browsers. Assume all credentials and session tokens were captured.
Check dark web sources. Stolen data from infostealers typically appears on criminal marketplaces within hours to days. Monitor infostealer channels to determine if and when data from your infection surfaces on dark web markets.
Track the infection timeline. Understand when the infection occurred and when it was detected. Any credentials used during that window should be considered compromised.
Consider downstream attacks. Infostealer infections often precede more damaging attacks. Threat actors use stolen credentials to gain initial access for ransomware deployment. Watch for unusual authentication patterns in the weeks following an infection. Your malware incident response plan should include monitoring for these secondary attacks.
The faster you detect an infection, the less data attackers can steal and the smaller your remediation scope.
Deploy behavioral detection. Signature-based antivirus misses new malware variants. Behavioral detection identifies suspicious activity patterns regardless of specific malware signatures.
Monitor for credential abuse. Sometimes the first sign of an infostealer infection is stolen credentials appearing on the dark web. Real-time monitoring of leaked credentials can alert you to infections that evaded endpoint detection.
Watch authentication patterns. Look for:
Check data exfiltration indicators. Infostealers must send stolen data somewhere. Monitor for:
Malware incident response has evolved. The traditional approach of “find the malware, clean the device, move on” leaves organizations exposed to credential-based attacks that can persist for months or years after the initial infection.
Complete malware remediation now requires addressing both the infected endpoint and the stolen authentication data. Your malware incident response playbook must account for both.
Effective malware incident response requires:
The organizations that get breached aren’t necessarily the ones with the weakest defenses. They’re often the ones that responded to an infection without addressing the stolen credentials that attackers continued to exploit.
Your malware incident response playbook is only as good as your ability to answer one question: “What was stolen, and have we revoked access to everything the attackers captured?”
If you can’t answer that question with confidence, your incident response isn’t complete.
Want to detect compromised credentials before attackers use them? Check your organization’s dark web exposure to see what data is already available to threat actors. Or book a demo to see how Breachsense monitors infostealer channels and criminal marketplaces in real-time.
Malware incident response is the coordinated process of detecting, containing, eradicating, and recovering from malware infections. It includes isolating infected systems, analyzing malware behavior, remediating compromised accounts, and implementing controls to prevent reinfection. Effective response addresses both device cleanup and stolen credential remediation.
The seven steps are: (1) Preparation with team roles and monitoring, (2) Identification of the threat and what was stolen, (3) Containment to stop lateral movement, (4) Eradication to remove malware, (5) Recovery to restore operations, (6) Credential and session remediation to revoke stolen access, and (7) Lessons learned to improve future response.
Isolate the infected system immediately by disconnecting from the network, but don’t power it off. Analyze the malware to understand what was stolen. Remove the infection, reset compromised passwords from clean devices, invalidate active sessions, and monitor dark web sources for stolen credentials appearing on criminal marketplaces.
Incident response is the full process of handling a security incident from detection through recovery. Malware analysis is one component of that process, focused specifically on understanding the malware’s behavior, capabilities, and indicators of compromise. Analysis informs response decisions but doesn’t encompass the full remediation effort.
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