First 24 Hours After a Cyberattack: Incident Response Guide

In the first 24 hours after a cyberattack, organizations must immediately isolate affected systems, preserve volatile forensic evidence by keeping devices powered on, and activate their incident response plan to verify the scope of the compromise. Promptly documenting the timeline and notifying relevant regulatory bodies, such as those governed by GDPR or PIPEDA, is essential to minimize legal and operational fallout.

The Critical Window of Incident Response

When a security breach is suspected, the initial reactions of your team can determine whether the event is a contained incident or a catastrophic loss. According to the National Cyber Threat Assessment 2025-2026, ransomware remains a primary threat to critical infrastructure, often involving sophisticated tactics like AI-driven social engineering and cryptocurrency-based extortion.

Modern attackers often gain quiet access to communication systems long before they deploy a payload, using that time to identify high-value data. Consequently, the first 24 hours are not just about stopping the attack; they are about understanding how deep the roots of the compromise go.

Immediate Technical Containment: What Not to Do

A common instinct during a cyberattack is to pull the plug or reboot the machine. However, guidance from the Canadian Centre for Cyber Security emphasizes that you must preserve volatile forensic evidence.

Follow these technical steps immediately:

Do NOT shut down the system: Powering down can wipe temporary memory (RAM) where malware signatures and encryption keys may reside.
Do NOT reboot: A reboot can trigger startup scripts that further propagate the attack or delete evidence.
Do NOT log out: Active sessions can provide vital clues for forensic investigators.
DO lock the system: Prevent further user interaction while keeping the current state intact.
DO disconnect from the network: If possible, disable the Wi-Fi or unplug the Ethernet cable to stop the lateral movement of the threat without killing the power.

Verifying the Scope of the Compromise

Once the immediate threat is isolated, you must verify the incident with your IT department or a specialized security partner. Documentation started in these early hours will be the foundation of your recovery. Note exactly when the compromise was first suspected, which specific devices or accounts are involved, and who had administrative access to those systems at the time of the event.

For businesses looking to identify these gaps before an incident occurs, penetration testing and vulnerability assessments are essential proactive measures.

Navigating Global Regulatory Requirements

Reporting is not just a best practice; in many jurisdictions, it is a legal mandate. Under the Personal Information Protection and Electronic Documents Act (PIPEDA), organizations must report breaches that pose a "real risk of significant harm" to the Office of the Privacy Commissioner.

Globally, frameworks like the GDPR require notification within 72 hours, meaning the data gathered in your first 24 hours is crucial for meeting these tight deadlines. Gpenda Technologies recommends maintaining a centralized log of all breaches, even those that do not meet the threshold for mandatory reporting, to demonstrate due diligence to regulators and stakeholders.

Addressing the Ransomware Threat

Ransomware is a common threat for small and medium-sized businesses, frequently delivered via phishing attachments or spoofed websites according to Get Cyber Safe. If you find your data encrypted, the first 24 hours should involve:

Identifying the strain: Understanding the specific ransomware can help determine if a public decryptor exists.
Evaluating backups: Determine the integrity of your offline or cloud-based backups. Never connect a backup drive to a potentially infected network.
Consulting Law Enforcement: Reporting the attack to local authorities helps track global trends in cybercrime and may provide access to specialized recovery resources.

Communicating the Incident

Internal and external communication must be handled with precision. Within the first day, notify your legal counsel and insurance provider. Informing affected individuals is often required by law, but the timing must be balanced so that you do not provide incomplete or inaccurate information that causes unnecessary panic. Gpenda Technologies works with teams to ensure their communication strategies align with both technical recovery and regulatory compliance.

Frequently asked questions

Should I shut down my computer if I suspect a cyberattack?

No. You should lock the screen and disconnect the network cable, but do not shut down or reboot. Keeping the system powered on preserves volatile forensic evidence in the RAM that is lost during a power cycle.

How do I know if a breach is mandatory to report?

Under frameworks like PIPEDA, you must report a breach if it poses a real risk of significant harm to individuals. This includes risks like identity theft, financial loss, or damage to reputation. Other global regulations, such as GDPR, have their own specific reporting thresholds.

What is the most common way ransomware enters a business?

Most ransomware is delivered through phishing emails containing malicious attachments or links to spoofed websites. Attackers also exploit unpatched software vulnerabilities to gain initial access to a network.

Can AI help prevent these attacks in the first 24 hours?

While AI is used by attackers to automate threats, defensive AI and machine learning tools can help detect anomalous behavior early, allowing for faster containment within those critical first few hours.

If you need immediate assistance or want to harden your infrastructure against future threats, please contact us or start a request today.

Sources

Facts checked against live sources on 2026-10-27.

The First 24 Hours: A Strategic Incident Response Protocol for Cyberattacks