BEST PRACTICES How to Anonymize Data? The Most Common Mistakes

In the age of digital transformation, protecting personal data has become not only a legal obligation but also a pillar of customer trust. With the implementation of the GDPR (General Data Protection Regulation, Regulation (EU) 2016/679), organizations—both public and private—are required to effectively safeguard sensitive information. One of the most crucial processes in this area is data anonymization.

But what exactly is anonymization? When should it be applied, and how can the most common mistakes be avoided? This article addresses these questions.

Anonymization is the process of transforming personal data in such a way that it becomes impossible to identify the individual to whom the data refers—either directly or indirectly. Unlike pseudonymization, anonymization is irreversible. This means that once the process is completed, the data is no longer considered “personal data” under the GDPR.

Data that may be subject to anonymization includes:

• Name, surname, national ID number (PESEL), address
• Bank account numbers, health information
• Location data, IP addresses
• Biometric data (e.g., fingerprints, retinal scans)

According to the GDPR and the Polish Act on Access to Public Information, anonymization becomes mandatory when data is made public but is not essential to the purpose of processing. Examples include:

• Publication of court rulings
• Sharing minutes of city council meetings
• Financial reports containing personal data
• Medical documentation shared for scientific purposes

Despite good intentions, many organizations still make serious mistakes during the anonymization process. Here are the most common ones:

1. Incorrect Identification of Sensitive Data

Many systems detect only obvious identifiers like PESEL numbers, names, or emails, while overlooking more subtle identifying data—such as policy numbers, signature information, or location data.

2. Overgeneralized Anonymization or Excessive Redaction

Sometimes documents are overly redacted, stripping them of meaningful content. Other times, anonymization is too superficial, leaving data that can still lead to identification.

3. Lack of Standardization

When there is no standardized anonymization process, employees apply different methods, increasing the risk of errors and inconsistencies across documents.

4. Improper Processing of Scanned Documents

It’s often overlooked that scanned documents are images—their content must be recognized via OCR (Optical Character Recognition). If the technology is inadequate, data may be missed.

5. No Final Validation

After anonymization, documents are not re-analyzed, which can result in accidental disclosure of information.

• Identify sensitive data — even in less obvious places — not just in tables or forms but also in descriptions and notes.
• Set anonymization rules — define templates and criteria for different document types.
• Automate the process — especially when handling large volumes of data.
• Use OCR tools — to recognize data in scanned documents (even low-quality) and images.
• Verify results — before sharing data, ensure the anonymization was correctly done.

This is where Redact comes in—a sophisticated tool for automatic data anonymization, designed for businesses and public institutions. Redact supports the full GDPR-compliant process and offers:

• Automatic recognition of 23 types of sensitive data in 80 languages
• Powerful OCR that works even on low-quality and multilingual scans
• Support for 25 file formats (PDF, DOCX, JPG, etc.)
• Editable drafts of anonymized files
• Ready-made redaction templates (with AI support)
• Flexible redaction patterns
• Full audit trail and access control

Thanks to these features, Redact not only automates the process but also reduces the risk of human error. Its team collaboration capabilities, redaction undo options, and context-aware anonymization (e.g., Jan, Jana, Janowi) make it a unique tool.

Example: A law firm using Redact can prepare hundreds of court documents for publication within minutes, eliminating the risk of disclosing parties’ personal information.

Anonymization is not just about regulatory compliance—it’s a sign of responsible privacy management. In the data-driven era, where every leak can mean a PR crisis or financial penalties, investing in proven tools and standards is essential.

Remember: it’s not enough to just start anonymizing—you have to do it right. And for that, you need technology that won’t let you down. That technology is Redact.