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Knowledge base Updated: February 5, 2026

Data leakage - What it is, how it happens, how to check and where to report it

Learn what a data leak is, how it happens, how to find out if you are affected, and where to report the incident.

Marcin Godula Marcin Godula

Data leaks have become one of the biggest challenges of modern business. The costs of a single incident are high, and detecting and containing a leak often takes many months. However, in addition to the immediate financial losses, organizations face the long-term consequences of loss of customer trust and potential regulatory penalties.

In this comprehensive guide, cybersecurity experts examine all key aspects of data leaks. We present a comprehensive approach to the problem - from understanding leakage mechanisms, to detection and response methods, to prevention and risk minimization strategies. Special attention is paid to practical tips and best practices that will enable organizations to more effectively protect themselves from data leaks and meet legal and regulatory requirements.

Whether you’re a security professional, IT manager or board member responsible for protecting your organization’s data, you’ll find concrete solutions and recommendations backed by the latest industry research and statistics. Learn a comprehensive approach to data leakage and how to effectively protect your organization from this growing threat.

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What is a data leak?

A data leak is a security incident in which confidential, protected or sensitive information is exposed to unauthorized individuals or systems. Contrary to popular belief, not every data leak is the result of a cyber attack - it can also occur as a result of human error, misconfiguration of systems or procedural negligence.

The cost of a data leak is high. What’s more, identifying and stopping a data leak often takes organizations many months. This shows how important it is to implement appropriate mechanisms for monitoring and responding to security incidents.

Data leakage can take many forms - from accidentally sending a document to the wrong recipient, to unsecured databases publicly available on the Internet, to malicious actions by employees or sophisticated hacking attacks. It is crucial to understand that leaks can involve digital data as well as physical documents.

In the legal context, it is particularly important to distinguish between a simple data leak and a data breach under the RODO. The latter is subject to specific regulations and requires specific actions on the part of the data controller, including a potential notification to the supervisory authority.

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What is the difference between a data leak and a data breach?

Although the terms “data leak” and “data breach” are often used interchangeably, there are important legal and technical differences between them. A data breach is a broader term that encompasses any event leading to the accidental or unlawful destruction, loss, modification, unauthorized disclosure of or access to personal data.

In practice, this means that any leakage of personal data is a breach, but not every breach involves a leak. For example, ransomware encrypting data without exfiltrating it is a breach of data availability, but not necessarily a data leak. A large number of data protection violations are reported every year, and a significant share of them are actual data leaks.

The scope of responsibility and required actions is also an important difference. In the event of a data breach, the controller has a legal obligation to conduct a detailed risk analysis and potentially notify both the supervisory authority and data subjects. A data leak not subject to the RODO may not require such actions, although good business practices often suggest a similar approach.

Technically, a breach can also include situations of temporary data unavailability or loss of integrity, while a leak always involves compromising the confidentiality of information. This distinction is crucial when planning incident responses and implementing security mechanisms.

What are the most common causes of data leakage?

Human error remains the leading cause of data leaks, accounting for the vast majority of incidents. This ranges from inadvertent actions, such as accidentally sending documents to the wrong recipients, to knowingly violating security procedures to “make things easier” for oneself.

The second most common cause is configuration errors in systems and applications. Particularly dangerous are poorly secured cloud databases and S3 buckets, which regularly lead to massive data leaks. Improper cloud configuration is responsible for some data leaks in corporate environments.

Hacking attacks, contrary to popular belief, are only in third place. Particularly dangerous are attacks using phishing and social engineering techniques, which often lead to the hijacking of users with high privileges. Many data leaks related to cyber attacks begin with a successful phishing attack.

Malicious employees (insider threats) are also becoming a growing problem. Most departing employees take company data with them, often unknowingly violating security policies and regulations. Even worse, some of them admit to intentionally taking out information that may be useful in their new job.

What types of data are most often leaked?

Personal data is the most commonly compromised category of information, with basic identifying information like names, email addresses and phone numbers being particularly vulnerable. This type of data accounts for the vast majority of all leaks. This high percentage is due to the fact that virtually every organization processes this information, and its value on the black market remains steadily high.

The second most commonly stolen type of data is credentials - passwords, access tokens and API keys. Compromising them is particularly dangerous, as it often leads to cascading security breaches. The average user uses the same password for many of their accounts, making it likely that a leak of login data from one service can lead to the compromise of many others.

Financial data, including credit card numbers, bank account data or transaction information, ranks third in terms of frequency of leaks. Although they are usually better protected than master data, their high market value makes cybercriminals willing to devote more resources to acquiring them. The time from the leak of credit card data to the first attempt to use it illegally is often very short.

Leaks of medical data and health information are also increasingly common. This type of data is particularly valuable to criminals because of its potential to be used for blackmail or extortion. In 2023, there was a significant increase in medical data leaks compared to the previous year, making it the fastest-growing category in terms of the number of incidents.

How can data leakage occur?

Unauthorized access to IT systems remains a major vector for data leakage. Attackers use a variety of techniques, from simple brute force attacks, to exploitation of known vulnerabilities, to advanced attacks using zero-day exploits. Many data leaks occur through this route.

Phishing and social engineering are the second most popular vectors for data leakage. Criminals are improving their techniques, using artificial intelligence to create more convincing messages and better target potential victims. Spear phishing targeting high-level employees is particularly dangerous - the probability of success of such an attack is high.

Accidental sharing of data by employees is the third most common cause of leaks. This includes both improper permission settings in cloud systems and unknowingly sending confidential information to the wrong recipients. The average organization experiences many incidents of accidental sharing of confidential data, some of which represent a potential risk of a serious security breach.

Malware, especially data exfiltration ransomware (double-extortion ransomware), is a growing threat. Criminals not only encrypt data, but also steal it before encryption, increasing the pressure on victims. The vast majority of ransomware attacks include a data exfiltration component, and this share is growing.

How do I check if my data has been leaked?

Verifying a potential data leak requires a systematic approach and the use of a variety of monitoring tools. A basic step is to regularly check specialized data leak monitoring services, such as Have I Been Pwned or BreachAlarm. Users who regularly monitor their online data have a significantly greater chance of detecting the compromise of their information early.

Organizations should implement advanced dark web monitoring systems that automatically scan hacker forums and marketplaces for signs of leaked corporate data. The time between the appearance of stolen data on the dark web and its use by criminals is often short, highlighting the importance of quick detection.

Another important element is monitoring network traffic for abnormal data transmission patterns. SIEM (Security Information and Event Management) systems can detect anomalies that indicate potential data exfiltration. Organizations using advanced SIEM systems detect data leaks much faster than those relying on basic monitoring alone.

Regular auditing of permissions and access to IT systems can reveal unauthorized changes indicating data compromise. A significant share of detected data leaks are identified during routine privilege reviews. This process should include both local systems and cloud services.

What to do if a data leak is detected?

Immediate response to a detected data leak is key to minimizing potential damage. The first step should be the creation of an incident response team to coordinate all recovery efforts. Organizations with a dedicated CERT/CSIRT team significantly reduce the average cost of a data leak compared to companies without such structures.

Documenting and securing digital evidence must begin as soon as possible after an incident is detected. This includes taking forensic images of systems, securing logs and documenting the chronology of events. Most legal cases involving data leaks fail due to insufficient or improperly secured evidence documentation.

Conducting a detailed analysis of the scope of the leak is essential to determine the scale of the incident and the potential impact on the organization. It is necessary to determine exactly what data has been compromised, who is affected, and what the consequences of its disclosure may be. Fully determining the scope of a data leak often takes organizations many weeks, which significantly affects the effectiveness of remediation efforts.

After the initial analysis, it is necessary to implement immediate countermeasures, such as changing passwords, revoking certificates and blocking compromised accounts. In many data leak cases, quick remedial actions made it possible to significantly reduce the extent of the compromise and prevent secondary security incidents.

Where should I report leaked personal information?

Reporting a personal data leak is subject to strict regulations, and the main addressee of such notification is the Office for Personal Data Protection (OPA). A data controller is obliged to notify the supervisory authority within 72 hours of discovering a breach, as long as the breach is likely to result in a risk of violating the rights or freedoms of individuals. A significant share of breach notifications are not made within the required time.

In the case of incidents involving public sector entities or critical infrastructure operators, it is also necessary to notify the NASK CSIRT (National Cyber Security Center). Coordination between the DPA and the NASK CSIRT allows for more efficient incident management - the response time is shorter than in cases reported to only one authority.

Organizations operating in the financial sector have an additional obligation to report leaks to the Financial Supervisory Commission (FSC). This is especially true for banks, insurance companies and other financial institutions. The number of security incident reports in the financial sector is clearly growing.

If the leak involves telecommunications data, the Office of Electronic Communications (UKE) should also be notified. In the case of telecom operators, a significant share of data leaks are related to errors in billing systems or customer databases, which requires special attention from the regulator.

At what time should data leakage be reported?

A key deadline under RODO is the 72-hour period for reporting a breach to the supervisory authority, calculated from the moment the breach is discovered. It is worth emphasizing that it is not the moment when the leak actually occurs, but the moment when the organization detects it. Organizations that have implemented automated incident detection systems are able to meet this deadline in the vast majority of cases.

Additional, often shorter notification deadlines apply for certain economic sectors. For example, banks must inform the FSC of major security incidents within 24 hours. Only some financial institutions are able to meet this deadline, demonstrating the magnitude of the challenge in responding quickly to incidents.

In the event of a high risk of violation of the rights or freedoms of individuals, the controller is required to notify data subjects “without undue delay.” Practice shows that organizations need an average of 5 days to prepare and start the process of notifying the affected, which is often criticized as too long.

A delay in reporting a breach must be duly justified. The most common reasons for exceeding the statutory notification deadline are the complexity of the incident, difficulties in determining the scope of the breach, and problems with coordination between different departments of the organization.

Who is responsible for reporting a data leak?

The primary responsibility for reporting a data leak lies with the data controller, that is, the entity that alone or jointly with others determines the purposes and means of data processing. In practice, this means that in business organizations this responsibility lies with the board of directors, which should ensure that adequate procedures and resources are in place to handle such incidents. Companies where the board of directors is actively involved in cyber security issues record significantly fewer serious incidents.

The Data Protection Officer (DPO), if appointed in the organization, plays a key advisory role in the breach notification process. His or her responsibilities include assisting the administrator in assessing the risks associated with a breach and preparing appropriate documentation. Organizations with a DPO respond faster to data leakage incidents.

In the case of processors (processors), they are obliged to immediately notify the administrator of a detected breach. Practice shows that the average time between the processor’s detection of a breach and the administrator’s notification is 24 hours, although shorter deadlines are often set in entrustment agreements. Delays in communication between processors and administrators account for many cases where the statutory 72-hour deadline for breach notification is exceeded.

In multi-branch or multinational organizations, it is crucial to clearly define roles and responsibilities for breach reporting. Companies with a centralized security incident management system are significantly more effective in coordinating their response to a data leak, especially when the incident affects multiple jurisdictions.

How to protect against data leakage?

Implementing a comprehensive data protection strategy requires a multi-layered approach, starting with proper classification of information. Organizations that have conducted a thorough inventory and classification of data reduce the risk of major leaks significantly compared to companies without such practices. The classification process should be updated regularly, taking into account changing business needs and new types of data being processed.

Encryption of sensitive data, both at rest and during transmission, is a fundamental layer of protection. Organizations using advanced cryptographic solutions and proper key management significantly reduce the average cost of a potential data leak. It is particularly important to use end-to-end encryption for the most sensitive data and to rotate encryption keys regularly.

Access control based on the Principle of Least Privilege significantly reduces the potential scope of a data leak. Most major data leaks involve excessive user privileges. Implementing an identity and access management (IAM) system with automatic verification and revocation of privileges reduces the risk of internal leaks significantly.

Regular employee training in information security is key to minimizing the risk of data leakage. Organizations that conduct systematic awareness programs that include hands-on exercises and phishing simulations report significantly fewer incidents related to human error. Training that uses real-world examples of incidents and personalized threat scenarios is proving particularly effective.

What are the consequences of data leakage?

The consequences of a data leak are multifaceted and often long-term, going well beyond immediate financial losses. The total cost of a data leak for a large organization is high. Importantly, this cost takes into account not only the immediate costs associated with incident response, but also the long-term reputational and operational impacts.

Loss of customer trust is one of the most serious consequences of a data leak. Most consumers lose trust in organizations after a major data leak, and many of them share their negative experiences with other people. As a result, companies experience a drop in stock value after a leak is revealed, and fully rebuilding a reputation can take a long time.

Administrative penalties imposed by supervisory authorities can be particularly severe, especially in the context of RODO violations. In 2023, the total value of fines imposed in the EU for data protection violations exceeded €1.7 billion. It is worth noting that the amount of fines does not depend solely on the scale of the leak, but also on how the organization prepared for data protection and responded to the incident.

Operational costs for handling the aftermath of a leak often exceed original estimates. These include spending on digital forensics, notifying victims, providing credit monitoring and strengthening security systems. In addition, organizations often face legal and PR costs, which can run into the millions of dollars in the case of major leaks.

How do you recognize that a data leak has occurred?

Early detection of a data leak requires systematic monitoring of multiple indicators and anomalies in IT systems. Unusual patterns in network traffic, especially large data transfers at unusual times or to unknown locations, can be the first warning sign. In the vast majority of data leakage cases, unusual network traffic patterns had previously occurred that could have been detected with proper monitoring.

Unauthorized changes in user privileges or sudden modifications to databases should arouse the security team’s immediate vigilance. In a significant share of data leaks, they were preceded by suspicious changes in permissions that were not noticed or verified in time. SIEM systems configured to detect such anomalies increase the chance of early incident detection significantly.

Unusual user behavior, such as logging in at unusual times, accessing rarely used resources or downloading documents en masse, can signal a potential leak. Organizations using sophisticated User Behavior Analytics (UBA) systems are able to detect suspicious activity much earlier than those relying on traditional monitoring.

External signals, such as the appearance of an organization’s data on the dark web or an unusual increase in the number of login attempts to systems, can also indicate a leak. In organizations that do not have sophisticated dark web monitoring and threat analytics systems, it often takes many months from the time of a leak to its detection.

What tools help detect data leakage?

Security Information and Event Management (SIEM) systems are an essential tool in the arsenal of security teams, aggregating and analyzing logs from various sources in real time. Advanced SIEM implementations using machine learning can detect subtle anomalies indicating potential data leakage. A properly configured SIEM system can significantly reduce leak detection time compared to traditional monitoring methods.

Data Loss Prevention (DLP) solutions act as gatekeepers for sensitive data, monitoring and controlling its flow within an organization’s network. Modern DLP systems use advanced algorithms to identify and classify sensitive information, blocking unauthorized attempts to exfiltrate it. Organizations using next-generation DLP solutions are able to prevent the vast majority of inadvertent data leaks by employees.

Dark web monitoring tools are becoming an increasingly important part of leak detection strategies. Automated scanners scour hacker forums, marketplaces and criminals’ communication channels for signs of stolen data. Organizations using professional dark web monitoring services detect leaks much earlier than those relying solely on internal detection mechanisms.

UEBA (User and Entity Behavior Analytics) systems use advanced analytics to profile normal user and system behavior, enabling the detection of deviations that could indicate a leak. In practice, organizations using UEBA experience significantly fewer false alarms compared to traditional anomaly detection systems, with a significant increase in actual incident detection.

How to conduct a quick identification of the cause of the leak?

A methodical approach to incident analysis begins with securing digital evidence and creating a timeline of events. It is crucial to use digital forensics tools to reconstruct the sequence of activities leading up to the leak without compromising the integrity of the evidence. Organizations using standard digital forensics procedures identify the source of a leak much faster than those operating ad hoc.

Analysis of system and network logs should focus on identifying the starting point of compromise (patient zero). Log visualization and network analytics tools help quickly catch anomalies and links between seemingly unrelated events. Using advanced log analysis tools significantly reduces the time to identify the cause of a leak.

By correlating data from various sources, including security systems, applications and infrastructure, a complete picture of an incident can be created. SOAR (Security Orchestration, Automation and Response) platforms automate the process of data collection and analysis, speeding up the identification of the cause of a leak. Organizations using SOAR reduce the average incident response time significantly compared to manual analysis.

Threat Intelligence provides the context necessary to understand the nature of the attack and potential perpetrators. Analysis of indicators of compromise (IoC) combined with data on known techniques, tactics and procedures (TTP) of criminal groups allows for faster identification of the method of leakage. Organizations actively using threat intelligence are able to determine the cause of a leak faster than those relying solely on internal analysis.

Summary

To summarize the above chapters, it is worth highlighting some key aspects related to data leaks that every organization should consider in its cyber security strategy.

Above all, data leakage is not just a technical problem, but a complex organizational challenge requiring a holistic approach. Effective protection against leaks requires a combination of appropriate technology, procedures and employee training. It is especially important to understand that even the best technical safeguards can fail if the organization does not ensure an adequate security culture.

From a legal and regulatory perspective, it is crucial for organizations to be prepared to meet breach reporting requirements. The 72-hour deadline for reporting a leak to the DPA may seem long, but without proper preparation and tested procedures, meeting this deadline is a major challenge. Organizations should regularly test their incident response procedures through exercises and simulations.

In terms of tools and technologies, it is worth noting the growing importance of solutions using artificial intelligence and machine learning in detecting potential leaks. Next-generation SIEM systems, advanced DLP or SOAR platforms not only increase the effectiveness of incident detection, but also significantly reduce the number of false alarms, allowing security teams to focus on real threats.

Finally, the importance of a proactive approach to data security cannot be overstated. Regular audits, penetration testing, bug bounty programs or continuous threat monitoring can identify and eliminate potential security vulnerabilities before they are exploited by attackers. Investing in prevention is always more cost-effective than incurring the costs of an actual data leak.

Organizations that treat data security as an ongoing process rather than a one-time project are much better prepared for today’s threats. The key to success is to build an organizational culture in which every employee understands his or her role in protecting data and can respond appropriately to potential security incidents.

Keep in mind that in today’s increasingly digital world, data leakage can have disastrous consequences not only for the organization, but most importantly for the individuals whose data has been compromised. That is why it is so important to treat data protection as one of the fundamental priorities in any organization’s strategy.

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