Wednesday 12 September 2018

Beware! Windows Explorer's handling of .zip files is buggy!

Tim contacted me today to make me aware of a problem with Windows 10 Explorer's handling of .zip file extraction.

He told me that he had a problem when using WSUS Offline Update. He downloaded the .zip file onto the \_ISO\WINDOWS\installs\ folder but when he tried to use WSUS, he  found it would not work correctly because Windows Explorer had changed the modification date of all the extracted files.

I checked this out by downloading the WSUS Offline Update download file and this is what I discovered...

If you open the .zip file by double-clicking on it, Windows 10 Explorer displays the correct 'Modified' date for the files within:

So you might expect that if you extracted these files, you would get the same 'Date modified' date?

However, when you extract the files, either using right-click - Extract All or by using cut-and-paste, the  modified date of all the files is changed to the current date and time:

Note the 'Date modified' has been changed.
In addition, Windows Explorer also tags the files with a 'Block' tag to mark each file as a downloaded file.

However, if you use 7zip or WinRar to unzip the files, the Modified date is preserved and the files are not tagged with a 'Block' tag.

So, this behaviour of Windows Explorer can have unwanted side effects. Many utilities use the 'Modified date' to decide whether or not to update it's files, including the E2B Update scripts and WSUS Offline Update.

In the case of E2B (if you download the .zip file and run the update script), the affect will be that all the E2B files on your USB drive will be updated, which does no harm but obviously will take longer.

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