Your medical images contain more than just scan results. When you upload them to a DICOM file viewer online, you’re sharing patient names, birthdates, Social Security numbers, and detailed medical histories.
Our privacy audit reveals alarming gaps in how free online DICOM viewers handle this sensitive information.
The Hidden Data in Your Medical Images
DICOM files aren’t just pictures. They bundle your actual scan image with massive amounts of metadata that includes personal details.
Think of it like a digital envelope containing both your X-ray and your entire medical record.
Recent research shows that over 3,800 DICOM servers worldwide are exposed on the internet, with 30% actively leaking sensitive patient data.
That means roughly 1,159 servers are broadcasting private medical information to anyone who knows how to look.
The exposed data includes patient names, addresses, phone numbers, and sometimes Social Security numbers.
But it gets worse – researchers estimated that this vulnerability has exposed 59 million records over 30 years, including 16.1 million personally identifiable records.
Free DICOM Viewers: Privacy Promises vs Reality
We tested popular free online DICOM viewers to see how they actually handle your data. The results were mixed at best.
Local Processing Claims
Many viewers claim they process files “locally” on their device. IMAIOS DICOM Viewer documentation state,s “All operations are conducted locally on the user’s device, ensuring that no files are uploaded to external servers”. This sounds reassuring, but our audit found several issues:
The Good News: True local processing means your files never leave your computer. The viewer runs entirely in your browser, similar to opening a document in Microsoft Word.
The Reality Check: Not all “local processing” claims are accurate. Some viewers still transmit file metadata to their servers for “analytics” or “performance optimization.”
Cloud-Based Viewers: Convenience vs Privacy
Cloud-based DICOM viewers offer powerful features and cross-device access, but they require uploading your files to their servers.
PostDICOM’s cloud-based system stores medical records on healthcare cloud-based PACS servers with SSL-encrypted connections, but you’re still trusting a third party with sensitive data.
| Viewer Type | Data Location | Privacy Level | Features |
| Local Processing | Your Device Only | Highest | Basic viewing, measurements |
| Cloud-Based | Third-party Servers | Medium to High | Advanced tools, collaboration, and storage |
The Vulnerability Epidemic
The DICOM standard itself has severe security limitations. According to the DICOM Standards Committee, “the actual security and privacy depends entirely on the implementation of the standard,” meaning it’s up to each software maker to add protection.
Recent security audits found critical vulnerabilities in popular viewers:
- MicroDicom DICOM Viewer had a high-severity vulnerability (CVE-2025-5943) with a CVSS score of 8.8 out of 10, allowing remote attackers to execute malicious code
- RadiAnt DICOM Viewer addressed a vulnerability in their update mechanism that could allow attackers to manipulate content
Here’s what makes this particularly dangerous: Healthcare data breaches affected 276,775,457 individuals in 2024 alone – that’s an average of 758,288 records breached every single day.
What Actually Happens to Your Data
Immediate Upload Risks
When you upload a DICOM file to any online viewer, several things happen instantly:
- File transmission – Your complete file, including all metadata, travels across the internet
- Server processing – The receiving server must decode and analyze your file
- Temporary storage – Most services create temporary files during processing
- Analytics collection – Many free services collect usage data tied to your files
Long-term Storage Concerns
Even viewers claiming “no storage” often keep data longer than expected:
- Cache files for faster loading on repeat visits
- Analytics data linking your IP address to file types viewed
- Error logs that might contain file metadata
- Backup copies on multiple servers for redundancy
Third-party Integration
Free online viewers often rely on external services for core functionality. Security testing revealed that web applications accounted for 96% of discovered vulnerabilities, mostly from basic misconfigurations and exposed personally identifiable information.
The Anonymous Uploading Myth
Many services promise to “anonymize” your files automatically. But anonymization isn’t perfect:
What gets removed: Patient names, birthdates, ID numbers from obvious fields
What often stays: Embedded text in images, study descriptions, referring physician names, institutional identifiers
DICOM anonymization requires transforming both direct identifiers like patient names and indirect identifiers like demographics, plus potentially removing burnt-in text from images.
The problem? Automated anonymization misses context-dependent information that humans would catch.
Safer Alternatives for Medical Professionals
Desktop DICOM Viewers
Best for: Maximum privacy and control
Recommended: RadiAnt, Horos, MicroDicom (updated versions)
Why: Files never leave your computer
Local Processing Web Viewers
Best for: Quick viewing without installation
Look for: Viewers that explicitly process files in your browser only
Verify: Check browser developer tools to confirm no network uploads
Institutional Solutions
Best for: Healthcare organizations Recommended: PACS-integrated viewers, institutional licenses Why: Professional support, compliance features, audit trails
| Solution Type | Privacy Score | Convenience | Cost | Best For |
| Desktop Software | 9/10 | Medium | Free-$200 | Individual use |
| Local Web Viewers | 8/10 | High | Free | Quick access |
| Institutional PACS | 10/10 | High | $1000+ | Healthcare facilities |
Red Flags to Avoid
When evaluating any DICOM viewer, avoid services that:
- Require account registration for basic viewing
- Don’t clearly explain where your data goes
- Offer “free” advanced features without obvious revenue sources
- Lack HTTPS encryption on their website
- Don’t provide privacy policies or terms of service
- Request unnecessary permissions or data
Bottom Line: Your Data, Your Choice
Healthcare organizations must actively implement security measures to protect patient data, including encryption, access controls, and audit trails. But as an individual, you have the power to choose how your medical data gets handled.
The safest approach? Use desktop DICOM viewers for sensitive files. When you need the convenience of online viewers, choose services that process files locally in your browser and have transparent privacy practices.
Your medical images contain a lifetime of sensitive information. In an era where healthcare data breaches affected 82% of the U.S. population in 2024, protecting that information isn’t just smart – it’s essential.
