What to look for after a cybersecurity incident in your company

Discovering that your organization has just suffered a cybersecurity incident It's not exactly the best way to start the day: systems locked, services down, calls from worried customers, and the tech team looking terrified. But beyond the initial shock, what really makes the difference is what you do in the following hours: what you look into, who you notify, what you keep as evidence, and how you restore operations without leaving any openings for the attacker.

Respond with a cool head, speed and method This is key to ensuring an attack remains a serious scare and doesn't escalate into a financial, legal, and reputational disaster. In the following lines, you'll find a comprehensive guide, based on best practices for incident response, digital forensics, and business continuity planning, covering everything you should review after a cybersecurity incident and how to organize that review to learn from the experience, strengthen defenses, and comply with legal obligations.

What really happened: Understanding the incident and its seriousness

Before touching anything blindly, you need to understand what kind of attack you're facing.Ransomware that encrypts critical servers is not the same as a silent intrusion to steal data or unauthorized access to a corporate website. Correct identification determines everything that follows.

One of the first tasks is to classify the incident depending on the predominant attack: ransomware, theft of confidential information, compromise of corporate accounts, website modification, exploitation of vulnerabilities, etc. As the analysis progresses and affected assets are discovered, the initial classification often changes, so it is advisable to document this evolution.

It is also crucial to locate the input vectorPhishing messages with malicious attachments, fraudulent links, infected USB drives, RDP exposed to the internet, unpatched server vulnerabilities, stolen credentials, cloud misconfiguration… Identifying this access point allows you to better define the scope and, above all, close the door to prevent it from happening again.

Another aspect worth examining closely is whether the attack appears targeted or opportunistic.Mass campaigns of generic emails, automated scans for known vulnerabilities, or bots exploiting exposed services usually indicate a random attack. However, when detailed knowledge of the environment, specific references to the company, or the use of industry-specific tools are observed, it is likely a targeted attack.

From there, all potentially compromised assets must be listed.: workstations, Linux serversDatabases, cloud services, business applications, mobile devices, and any system that shares a network or credentials with the initially affected team. The more accurate this inventory, the easier it will be to define the true scope of the incident and prioritize the response.

Collect and preserve evidence without compromising the proof

Once the incident is detected, the natural temptation is to format, erase and start from scratchBut that's usually a major mistake from a forensic and legal standpoint. If you want to file a complaint, make an insurance claim, or simply understand what happened, you need to preserve valid evidence.

The first step is to isolate the affected systems without abruptly shutting them down.To prevent data loss in memory or alteration of critical records, the usual procedure is to disconnect from the network, block remote access, and stop non-essential services, but keep the equipment powered on until forensic images can be obtained.

Creating full copies of disks and systems is a basic practiceIt is highly recommended to create at least two copies: one on a write-only medium (e.g., DVD-R or BD-R) for forensic preservation, and another on a new medium to be used for processing, analysis, and, if necessary, data recovery. Hard drives removed from the systems should be stored in a secure location, along with the copies created.

Key information must be documented for each medium used.Who made the copy, when, on what system, with what tools, and who subsequently accessed those media. Maintaining a rigorous chain of custody makes all the difference if this evidence needs to be presented later to a judge or an insurance company.

In addition to disk images, logs and traces must also be secured. of all types: system logs, applications, firewalls, VPNs, mail servers, proxies, network devices, EDR/XDR solutions, SIEM, etc. These logs serve both to reconstruct the attack and to identify lateral movement, data exfiltration, or attacker persistence.

It is advisable to assess as soon as possible whether to take legal action.In that case, it is highly recommended to have a specialized forensic expert who can direct the collection of evidence, use appropriate tools, and prepare legally valid technical reports. The sooner they are involved, the less risk there is of contaminating or losing useful evidence.

Incident documentation: what needs to be written down

While the attack is being contained and systems are being rescued, it's easy to overlook the documentation.But then it's missed both for later analysis and for complying with regulatory obligations. That's why it's important to write everything up from the beginning.

It is very useful to accurately set the date and time of detection.as well as the first observed symptom: alert from a security tool, performance anomalies, locked accounts, ransomware message, user complaints, etc. If known, the approximate time of the start of the attack or security breach should also be noted.

In parallel, a list of affected systems, services, and data must be compiled.indicating whether the assets are business-critical or support assets. This information will be essential for prioritizing recovery and calculating the economic and operational impact of the incident.

Every action taken during the response must be recorded.What has been taken offline, what password changes have been made, what patches have been applied, what services have been stopped or restored, what containment measures have been taken, and when. This isn't meant to be a novel, but rather a clear and understandable timeline.

It is also necessary to record the names of all the people involved. In crisis management: who coordinates, which technicians are involved, which business owners are informed, which external providers help, etc. This then helps to review the team's performance and the suitability of the roles defined in the response plan.

One aspect that is sometimes forgotten is to keep a copy of relevant communications.Emails exchanged with clients, rescue messages, conversations with the insurer, exchanges with authorities, internal chats about critical decisions, etc. This information can be valuable for forensic investigations, for demonstrating due diligence to regulators, and for improving crisis communication protocols.

Notifications to agencies, clients and involved third parties

When the initial dust cloud begins to settle, it's time to notify the appropriate person.It is not an optional matter: in many cases the regulations require it, and in others transparency is vital to maintain trust.

If the incident involves personal data (customers, employees, users, patients, students…), it is necessary to review the obligations under the General Data Protection Regulation (GDPR) and local legislation. In Spain, this means notifying the Spanish Data Protection Agency (AEPD) when there is a risk to the rights and freedoms of individuals, usually within a maximum of 72 hours from becoming aware of the breach.

When the incident may constitute a crime (ransomware, extortion, fraud, theft of sensitive information, threats to critical infrastructure), it is advisable to report these incidents to the State Security Forces. In Spain, units such as the National Police's Technological Investigation Brigade or the Guardia Civil's Telematic Crimes Group typically intervene, and they can also coordinate with international organizations.

At the state level there are specialized centers that are worth keeping an eye on., such as INCIBE-CERT for citizens and private entities, or other sector-specific CSIRTs. Informing them can provide additional technical support, access to intelligence on similar threats, decryption tools, or clues about ongoing campaigns.

Companies with cyber insurance policies should review the notification conditionsThis is because many insurers require to be informed within very tight deadlines and condition coverage on following certain response guidelines and using approved providers.

Finally, it's time to think about communication with customers, partners, and employees.If data has been compromised or critical services affected, it's preferable that employees be informed directly by the organization, rather than through leaks or press reports. Clear and honest messages, explaining what has happened in general terms, what information might be affected, what measures are being taken, and what steps are recommended for those affected, are usually the best strategy for protecting reputation.

To contain, isolate, and limit the attacker's advance.

As soon as it is confirmed that there is a real incident, a race against time begins to prevent the attacker from moving further, stealing more data, or causing additional damage such as encrypting backups or compromising more accounts.

The first step is to isolate the compromised systems from the networkThis applies to both wired and wireless connections. In many cases, simply disconnecting network interfaces, reconfiguring VLANs, or applying specific firewall rules to block suspicious communications will suffice. The goal is to contain the attacker without destroying evidence or indiscriminately shutting down systems.

Along with physical or logical isolation, it is essential to review remote access.VPN, remote desktops, third-party connections, privileged access, etc. It may be necessary to temporarily disable certain access until it is clear which credentials may have been compromised.

Blocking suspicious accounts and credentials must be done preciselyStarting with high-privilege accounts, exposed service accounts, users directly involved in the intrusion, or those exhibiting anomalous activity, it is advisable to enforce broad password changes once the situation is more under control, prioritizing critical accounts first.

A more technical step is to strengthen traffic segmentation and filtering To prevent lateral movement and command and control communications, firewall rules, IDS/IPS, EDR/XDR solutions, and other controls come into play, enabling the blocking of malicious domains, IPs, and traffic patterns identified during the analysis.

At the same time, backups must be safeguarded.If backups are online or accessible from compromised systems, there is a risk that they may also be encrypted or tampered with. It is recommended to disconnect them, verify their integrity, and reserve them for the recovery phase, once you are certain they are clean.

Digital forensics: reconstructing the attack and locating vulnerabilities

With the threat contained, the actual "digital forensics" part beginsThat meticulous work of reconstructing step by step what the attacker did, how he entered, what he touched, and how long he was inside.

Forensic analysis begins by processing the collected evidence.Disk images, memory captures, system and network logs, malware samples, modified files, etc., also learning from real-world incidents such as failures in EDR solutionsSpecialized tools are used to reconstruct timelines, track configuration changes, identify suspicious processes, and map unusual network connections.

One of the main objectives is to locate exploited vulnerabilities and security gapsThis could include outdated software, default configurations, unjustified open ports, accounts without two-factor authentication, excessive permissions, development errors, or network segmentation failures. This list of weaknesses will then form the basis for corrective measures, as well as tools for Application Security Posture Management (ASPM).

The analysis also determines the true scope of the attack.This includes determining which systems have actually been compromised, which accounts have been used, what data has been accessed or exfiltrated, and for how long the attacker has had the ability to move freely. In complex environments, this may require days or weeks of detailed review.

When there are indications of exfiltration, network and database logs are examined in greater depth. to quantify how much information has been leaked, to which destinations, and in what format. This information is crucial for assessing the legal and reputational impact, as well as the notification obligations to authorities and affected parties.

All this work is reflected in technical and executive reportsThese reports should explain not only the technical aspects of the attack, but also its implications for the business and recommendations for improvement. They serve as a basis for justifying security investments, reviewing internal processes, and strengthening staff training.

Assess damages, compromised data, and impact on the business

Beyond the purely technical aspects, after an incident, numbers and consequences need to be put on the table.That is, to assess the impact in operational, economic, legal and reputational terms.

First, the operational impact is analyzed.This includes: services that have been down, production interruptions, downtime of critical systems, delays in deliveries or projects, inability to invoice, cancellation of appointments or interventions, etc. This information is the basis for estimating losses due to business interruption.

Then the affected data must be examined very closely.: personal information of customers, employees, suppliers or patients; financial data; trade secrets; intellectual property; contracts; medical recordsAcademic records, and so on. Each type of data has different associated risks and obligations.

For personal data, the level of sensitivity must be assessed. (for example, health or financial data versus simple contact information), the volume of records exposed, and the likelihood of malicious use such as fraud, identity theft, or blackmail. This assessment determines whether to notify the Spanish Data Protection Agency (AEPD) and the affected parties, as well as what compensatory measures to offer.

Thirdly, the direct economic impact is calculated.These costs include external cybersecurity services, lawyers, crisis communication, system restoration, urgent acquisition of new security tools, overtime, travel, etc. In addition, there are indirect impacts, which are more difficult to measure, such as loss of customers, reputational damage, regulatory fines, or contractual penalties.

Finally, the reputational impact and stakeholder trust are assessed.This includes the reaction of customers, investors, partners, the media, and employees. A poorly managed incident, with little transparency or a slow response, can have a reputational cost that lingers for years, even if it was technically resolved correctly.

Secure recovery: restoring systems without reintroducing the enemy

Once it has been understood what happened and the attacker has been expelled, the phase of restarting the systems begins. and return to normal. Haste makes waste if you want to avoid reinfections or leaving backdoors active.

The first step is to define recovery prioritiesNot all systems are equally important for business continuity: it is necessary to identify which ones are truly critical (billing, orders, support systems, customer service platforms, basic communications) and restore them first, leaving those of a secondary or purely administrative nature for later.

Before restoring, the systems must be cleaned or reinstalled.In many cases, the safest option is to format and reinstall from scratch, then apply the patches and hardened configurations, rather than attempting to manually "clean" a compromised system. This includes carefully reviewing startup scripts, scheduled tasks, service accounts, registry keys, and any possible persistence mechanisms.

Data restoration must be done from verified backups. as uncompromised. To do this, backups are analyzed with anti-malware tools, and dates are reviewed to select versions prior to the start of the incident. Whenever possible, it is recommended to first restore in an isolated test environment and verify that everything works correctly and without signs of malicious activity.

During the return to production of systems and services, monitoring must be especially intensive.The goal is to immediately detect any attempt by the attacker to reconnect, anomalous activity, unexpected traffic spikes, or unusual access. Solutions such as EDR/XDR, SIEM, or managed monitoring services (MDR) greatly assist in this enhanced surveillance.

Take advantage of the reconstruction phase to improve security controls It's a smart decision. For example, password policies can be strengthened, the multi-factor authentication, strengthen network segmentation, reduce excessive privileges, incorporate application whitelists, or deploy additional intrusion detection and access control tools.

Lessons learned and continuous improvement following the incident

Once the urgency has passed, it's time to sit down calmly. and analyze what went well, what went wrong, and what can be improved. Treating the incident as a real training exercise is what truly raises the level of cybersecurity maturity.

It is usual to organize a post-incident review This meeting involves representatives from IT, security, business, legal, communications, and, if applicable, external vendors. It reviews timelines, decisions made, challenges encountered, bottlenecks, and blind spots in detection or response.

One of the outcomes of this review is to adjust the incident response plan.: redefine roles and contacts, improve communication templates, refine technical procedures, clarify escalation criteria, or add specific use cases (e.g., ransomware attacks, data leaks, or cloud incidents).

Another essential solution is to prioritize structural safety measures Based on the vulnerabilities detected: patch systems, strengthen configurations, segment networks, review firewall rules, implement MFA where it is not yet in place, limit remote access, apply the principle of least privilege, and improve the asset inventory.

At the same time, the incident usually highlights the need for more training and awareness.Phishing drills, practical response workshops, sessions on best practices for information handling, and tabletop exercises help staff know how to act and reduce the risk of human error that causes so many breaches.

Organizations with fewer internal resources may consider outsourcing managed services. such as 24/7 monitoring, managed detection and response (MDR), or external incident response teams that complement internal CSIRTs. This is especially relevant when continuous monitoring cannot be maintained or when environments are highly complex.

Ultimately, every incident that is thoroughly analyzed becomes a lever for improvement. This strengthens resilience, accelerates response capabilities, and reduces the likelihood of a similar attack being equally successful in the future. Viewing incident management as a continuous cycle of preparation, detection, response, and learning is what distinguishes organizations that merely "put out fires" from those that truly emerge stronger with each blow.

Maintaining a comprehensive view of what to look for after a cybersecurity incident —from identifying the attack to preserving evidence, communicating with third parties, secure recovery, and lessons learned— allows you to move from improvised panic to a professional and structured response, capable of limiting damage, complying with regulations, and tangibly strengthening the organization's security.

Related article:

What is a SOC (Security Operations Center): structure, hierarchy, and how it works?

Isaac

Passionate writer about the world of bytes and technology in general. I love sharing my knowledge through writing, and that's what I'll do on this blog, show you all the most interesting things about gadgets, software, hardware, tech trends, and more. My goal is to help you navigate the digital world in a simple and entertaining way.