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Causes for a bad or corrupt Zip file

Article ID: 35
Last updated: 11 Apr, 2012
Views: 105203

The Zip file format, which is open source, has a specific structure defined in the .ZIP Application Note. By definition, the information recorded in the two Zip file headers should be equivalent. In other words, information recorded about a file in the Central directory should match the information recorded about the same file in the Local directory. This information should also be accurate.

Due to the nature of an open source format, it is very possible for you to receive a Zip file where a simple header issue exists. This header issue may be a minor mistake caused by the application or process used to create the Zip file. However innocent the mistake may seem, WinZip will treat all header inconsistencies, inacurate data, and incorrect extensions as possible security risks and report to you that the Zip file is corrupt. You may want to try to repair your Zip file at some point, as some of these matters can be corrected using a Zip file fix routine.

In other cases when the data in a Zip file is damaged, it may not be possible to fix the Zip file and you will not be able to extract all of the files correctly, if at all. Damaged data can affect the entire Zip file, multiple member files, or just one member file.

There are many possible causes for data damage. Among the most common is a transfer error when downloading a Zip file from the internet. Such an error can introduce invalid data into a Zip file. Some other possible causes include exposure of media to excessive temperatures or magnetic fields and mechanical problems with disk drives.

The best solution to the problem of a damaged Zip file is to try to obtain another copy of the file. For example, use your backup copy of the file or get a new copy from the original source. If you obtained the Zip file by downloading it, then downloading it again may solve the problem.

If the damaged Zip file is on a removable disk, the removable disk may be physically damaged, or the data on it may have been corrupted. In these cases, the only completely reliable solution is to use another, undamaged copy of the disk or Zip file. There are, however, two other situations in which it may be possible to recover some files from a removable disk.

  1. The removable disk drive that you are using to unzip the Zip file may be malfunctioning. Try using a different disk drive, if possible.
  2. If the removable disk drive you are using to unzip the Zip file is not the same drive that was used to store the Zip file on the removable disk, and you have access to the original drive, try using this drive to unzip. It is possible that the original drive may be able to read the disk; if so, you can extract your files using this disk drive (and have your removable disk drives checked out - at least one of them may have a mechanical issue). Otherwise, the removable disk itself or the data on it is probably damaged.

Related Articles:
Methods to try fixing invalid Zip files with the command line add-on
Information about CRC errors (encountered when extracting files)
Zip file is damaged after uploading to an FTP server
Download results in a corrupt Zip file for some and not for others

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