File Corruption

What Is File Corruption?

File corruption is damage to a file's internal data — the bytes that make up the file's content or structural metadata — that causes the file to become partially or fully unreadable.

Levels of Corruption

Structural corruption — the file's internal index or directory is damaged, but the content data is intact. This is the most common and most recoverable type. Example: a PDF with a broken xref table that can be rebuilt.

Content corruption — the actual data (pixel values, text bytes) is damaged. Some data may be recoverable, but corrupted sections cannot be reconstructed. Example: random bytes overwritten in the middle of a JPEG.

Header corruption — the first bytes of the file (the header that identifies the file type) are damaged. The file appears to have the wrong type or no type at all. Example: a ZIP where the first 4 bytes are corrupted, so it cannot be identified as a ZIP.

Common Causes

1. Interrupted file transfer or download
2. Storage media failure (bad sectors on HDD, SSD, or USB drive)
3. Application crash during save
4. File system errors after unexpected shutdown
5. Virus or ransomware damage
6. Email server attachment modification

How to Detect Corruption

• File size is smaller than expected (truncated download)
• File produces an error on open in any application
• File opens in some applications but not others
• Content appears scrambled, blank, or partially rendered
• Checksum does not match the published value

Recovery Priority

Always attempt recovery in this order:

1. Re-download from the original source
2. Restore from a cloud backup (Google Drive, Dropbox version history)
3. Use a format-specific repair tool
4. Restore from a local backup

The best protection against corruption is maintaining multiple copies in geographically separate locations.