Compressed files that are larger than 4 KB may be corrupted when you create or update the files

After you install security update 920958 (MS06-049) on a computer that uses NTFS file system compression, compressed files that are larger than 4 kilobytes (KB) may be corrupted when you create or update the files.

This problem occurs because of a regression error in security update 920958 (MS06-049), dated August 8, 2006.

To resolve this problem, install security update 920958 (MS06-049). This new security update was released on September 26, 2006, and it addresses the problem that is described in the "Symptoms" section.

Update information

The following information applies to security update 925308. Security update 925308 has been replaced by security update 920958.

Note This update does not recover files that are already corrupted. If you created a backup before you installed security update 920958, you can recover the corrputed files from this backup.

To work around this problem, disable NTFS compression. This prevents future file corruption if you cannot install the security update that is discussed in security bulletin MS06-049 (http://www.microsoft.com/technet/security/Bulletin/MS06-049.mspx) . To disable NTFS compression for a folder, follow these steps:

1. Right-click the folder, and then click Properties.
2. Click the General tab, and then click Advanced.
3. Click to clear the Compress contents to save disk space check box.
4. Click OK two times.
5. If you are prompted, use one of the following methods:
   • Click Apply changes to this folder only to disable NTFS compression for the folder only. Use this option if you do not have a backup and if you want to try to manually recover data from corrupted files. When you select this option, new files that are added to the folder will be uncompressed. However, compressed files that are already in the folder will remain compressed.
   • Click Apply changes to this folder, subfolders and files to disable NTFS compression for the folder and subfolders and to uncompress all files. Use this option if you do not intend to manually recover data from corrupted files. When you select this option, new files that are added to the folder will be uncompressed. Additionally, compressed files already in the folder and in all subfolders will be uncompressed.
     
     Important If you uncompress corrupted files, you may be unable to manually recover data from the uncompressed files.
6. Click OK.

Note Administrators can use the /U switch together with the compact command-line command to uncompress files and to mark folders as uncompressed. For example, use the following command to disable NTFS compression for the C:\Test folder only:Use the following command to disable NTFS compression for the C:\Test folder and for all subfolders. Also use this command to uncompress compressed files in the folder and in all subfolders:For more information about how to use command-line switches together with the compact command, type the following at a command prompt:

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

Security bulletin MS06-049 has been updated to mention a revised update that includes hotfix 925308.

For more information about security update 920958, visit the following Microsoft Web site: