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I run Windows 10 on my desktop and it seems common now, and on all versions of Windows I've had throughout the years, that system files somehow magically become corrupt. Recent versions of Windows now come with a great tool "dism" that can find corrupt files and download replacements from Microsoft's servers, which solves a lot of issues. But my question is: why? And how?

Surely most of these are libraries that are read-only anyway? What on earth is happening that would make the files become corrupt?

closed as too broad by Xavierjazz, DavidPostill, magicandre1981, mdpc, nc4pk Jan 22 '16 at 2:28

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There are a few possibilities as to why a file can become corrupted.

Hard disk corruption

The most common cause would be that the harddisk has a bad sector. The more a system file is being read to, the more the state of a disk is read which simply causes wear. Now, it would take millions of reads before it could cause a bad sector, but it could happen.

System crash

A system crash while the file is opened for read and write could cause this problem too. Although most of the time, the file will be opened for read only, sometimes for unknown reasons, the file is being opened for read and write (usually to make sure the file is opened and a lock to the file is claimed). If a crash happens while this file was opened in read/write mode, it may lead to corruption.

Program error while updating

It is possible the file got corrupted while downloading it and then during the installation of the update it got replaced with a bad copy.

Version mismatch

It is possible a dll file is shared and there are more than one versions available. One program could expect an older version while another updated it to a newer version. The other program could claim the file to be broken somehow.

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Personally I rarely have any issues like that (and I'm often trying to break things). I have however worked in positions where it would be frequently seen. Usual causes for this would be:

  • An unexpected shutdown (often when combined with a Windows Update)
  • Problems during a Windows Update
  • Failing hardware
  • Virus activity
  • Blindly following instructions from the internet that tell you to 'download this DLL and overwrite your one in system32'
  • Trying to uninstall programs manually and messing something up
  • Installing somewhat dubious software packages (Registry Cleaners and the like)

It's hard to say for certain and no doubt there are other causes, after all, it's an unexpected behaviour, so it's usually caused by something unexpected.

As stated, I don't remember the last time I had a corruption so bad it caused me to have to reinstall anything. Usually I just get to a point where I've installed so many different programs I feel it's just unclean and make a decision to start afresh.

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