Why Does My File Say Corrupted?

File corruption happens when data within a file becomes unreadable or damaged, preventing software from opening or processing it correctly. Common causes include incomplete downloads, storage device failures, sudden power loss, malware infections, software bugs, and improper file transfers. Understanding why corruption occurs helps you recover files and prevent future data loss.

What Is File Corruption?

Files are sequences of binary data (1s and 0s) organized in specific structures. Each file format has a header that identifies the file type, followed by data sections containing actual content. Corruption occurs when any part of this structure becomes damaged, altered, or lost.

Types of corruption:

• Header corruption: File type can't be identified (often shows as "unknown file")
• Partial corruption: Some content accessible, other parts damaged
• Complete corruption: File entirely unreadable (often 0 bytes or garbage data)
• Structural corruption: File structure broken but some data recoverable

Top 10 Causes of File Corruption

1. Incomplete Downloads or Transfers

Most common for downloaded files. If a download is interrupted before completion—due to network issues, browser crashes, or clicking "Cancel"—the resulting file is incomplete and likely corrupted.

Signs of incomplete download:

• File size much smaller than expected
• File size exactly 0 KB
• Error message "file is not a valid [format]"
• Checksum or hash doesn't match original

2. Storage Device Failures

Hard drives, SSDs, USB drives, and SD cards can develop bad sectors—physical areas that can no longer store data reliably. Files stored on or crossing bad sectors become corrupted.

Warning signs of storage failure:

• Multiple files becoming corrupted simultaneously
• Clicking, grinding, or unusual noises from hard drives
• Frequent "disk read error" messages
• Files disappearing or showing wrong sizes
• Operating system crashes or freezes when accessing certain drives
• SMART errors reported by disk utilities

3. Sudden Power Loss or System Crashes

Files are most vulnerable during write operations. If power is lost or a system crashes while saving a file, the file can be left in an incomplete or corrupted state.

Particularly vulnerable moments:

• Saving large documents (Word, Excel, Photoshop)
• Rendering video or exporting projects
• Installing software updates
• Database write operations
• Copying or moving files between drives

Operating systems use write caching to improve performance, meaning data isn't immediately written to disk. This improves speed but increases corruption risk during unexpected shutdowns.

4. Malware and Virus Infections

Ransomware encrypts files making them appear corrupted. Other malware types can directly modify or damage files. Even antivirus software removing infections can sometimes damage files in the cleanup process.

Malware-related corruption signs:

• Many files corrupted simultaneously
• Files have changed extensions (e.g., .locked, .encrypted, .crypted)
• Ransom notes appearing on desktop or in folders
• File modification dates all changed to same time

For ransomware, do NOT pay ransom. Contact cybersecurity professionals and check if free decryption tools exist for your specific ransomware variant at NoMoreRansom.org.

5. Software Bugs and Compatibility Issues

Software errors can save files incorrectly or fail to complete write operations properly. Compatibility issues between different software versions can also cause apparent corruption.

Common scenarios:

• Opening Office 2024 files in Office 2010
• Software crashes during "Save As" operations
• File format conversion errors
• Beta or unstable software versions
• Saving to network drives with connectivity issues

6. Improper File System Operations

Removing USB drives without ejecting, force-shutting down computers, or interrupting file operations can corrupt files and even entire file systems.

7. File System Corruption

The file system (NTFS, FAT32, exFAT, ext4, APFS) organizes how files are stored. If the file system itself becomes corrupted, individual files may become inaccessible even if their data is intact.

File system issues can cause:

• Files showing as 0 bytes despite containing data
• Folders becoming inaccessible
• "The file or directory is corrupted and unreadable"
• Files appearing with garbled names (e.g., ?????.doc)

8. Network Transfer Errors

Files transferred over networks can be corrupted by packet loss, interrupted connections, or protocol errors. This is especially common with:

• Unreliable WiFi connections
• FTP transfers without resume capability
• Email attachments over poor connections
• Cloud sync services with connectivity issues

9. Physical Damage to Storage Media

Dropping hard drives, exposing USB drives to extreme temperatures, water damage, or magnetic interference can physically damage storage media and corrupt files.

10. Age and Data Degradation

Storage media doesn't last forever. Data can degrade over time, especially on:

• CD/DVD: 5-10 years typical lifespan (can be much less)
• USB flash drives: 10-year data retention when unpowered
• Hard drives: 3-5 years average before higher failure risk
• SSDs: Data degradation after years without power

How to Check If a File Is Truly Corrupted

Test 1: Try Opening in Different Software

Sometimes the issue is software-specific, not actual corruption. Try opening the file in alternative applications:

• Documents: LibreOffice, Google Docs, OnlyOffice
• Images: GIMP, Paint.NET, IrfanView, browser
• Videos: VLC, MPV, Media Player Classic
• Archives: 7-Zip, WinRAR, PeaZip

Test 2: Check File Size

Right-click the file and select Properties (Windows) or Get Info (Mac). Compare the file size to expected values:

• 0 bytes: File is empty, download/transfer was completely interrupted
• Unusually small: Incomplete download or partial corruption
• Expected size: Corruption may be minor or software-specific

Test 3: Open in Text Editor (Advanced)

Open the file in Notepad or TextEdit to view raw data. Look for:

• Recognizable headers: %PDF, PK, GIF89a indicates file type is correct
• All zeros or garbage: Severe corruption
• Readable text mixed with binary: Partial corruption, some recovery possible

Test 4: Use File Verification Tools

If checksums (MD5, SHA-1, SHA-256) are available from the source:

• Windows: certutil -hashfile filename SHA256
• Mac/Linux: shasum -a 256 filename
• Third-party: HashTab, MD5 & SHA Checksum Utility

If checksums don't match, the file is definitely corrupted or incomplete.

File Recovery Methods

Method 1: Use Built-in Repair Features

Method 2: Restore Previous Versions

Method 3: Specialized Repair Software

File-specific repair tools:

• Stellar Repair: For Office, PDF, Photo, Video files (paid)
• Kernel for Word/Excel/PowerPoint: Office file recovery
• DataNumen: Comprehensive file repair suite
• Remo Repair: Media file specialization

Free alternatives:

• OfficeRecovery Online: Free limited repair, pay for full recovery
• JPEG Repair: Free for some image corruption
• MP4 Repair: Free video file repair tools

Method 4: Re-download or Request Resend

Often the fastest solution. If possible:

• Re-download from original source
• Request sender to resend via different method (cloud link instead of email)
• Download from alternative mirrors or sources
• Check if cloud services have version history (Google Drive, Dropbox)

Method 5: Check and Repair Storage Device

Method 6: Professional Data Recovery

For critical files that can't be recovered through software:

• OnTrack: Industry leader, expensive but high success rate
• DriveSavers: Specializes in physical recovery
• Secure Data Recovery: Emergency services available

Professional recovery costs $300-$3000+ depending on severity. Get quotes from multiple services. Many offer "no data, no charge" policies.

Prevention Strategies

Implement 3-2-1 Backup Rule

• 3 copies of important data (original + 2 backups)
• 2 different storage media types (hard drive, cloud, NAS)
• 1 offsite backup (cloud or physically separate location)

Use Reliable Storage

• Replace hard drives every 3-5 years
• Use reputable brands (Western Digital, Seagate, Samsung, Crucial)
• Monitor SMART data with tools like CrystalDiskInfo
• Keep drives in temperature-controlled environments

Safe Computing Practices

• Always use "Safely Remove Hardware" for external drives
• Use UPS (Uninterruptible Power Supply) for desktop computers
• Save work frequently (enable auto-save in applications)
• Keep software updated to latest stable versions
• Run regular antivirus scans

Verify Downloads

• Check file sizes match expected values
• Verify checksums when provided
• Use download managers with integrity checking
• Download from official sources, not third-party mirrors

When Recovery Isn't Possible

Sometimes files are unrecoverable due to:

• Severe physical damage to storage media
• Complete data overwrite
• Encrypted by ransomware with no known decryption
• Multiple layers of corruption from repeated failures

In these cases, focus on preventing future data loss. Implement comprehensive backup strategies and consider file importance when deciding on backup frequency and redundancy.