This Windows Bug May Have Accumulated Junk Files on Your PC

Gavin Phillips 08-09-2016

Are you still running Windows 7, 8, or 8.1? Then you might have noticed your available hard drive space steadily decreasing, even if you have not downloaded or added any new files to your system. This accumulation of junk files is a symptom of the log-file compression bug, a problem that Microsoft has known about for over two years.


While Microsoft hasn’t released anything officially, you can manually fix this bug and release your much needed hard drive space.

The Log-File Compression Bug

This is a known issue affecting the Trusted Installer What Is TrustedInstaller & Why Does it Keep Me From Renaming Files? TrustedInstaller is a built-in user account in Windows 8, Windows 7, and Windows Vista. This user account "owns" a variety of system files, including some files in your Program Files folder, your Windows folder, and... Read More CBS logs in Windows 7, 8, 8.1, and 2008 R2, as well as potentially existing in other versions too.

The Symptoms

Thankfully, poster jwalker107 thoroughly described the symptoms of the bug on the Microsoft Answers forum:

I’ve had repeated instances where a Windows 7 x64 client runs out of hard drive space, and found that C:\Windows\TEMP is being consumed with hundreds of files with names following the pattern “cab_XXXX_X”, generally 100 MB each, and these files are constantly generated until the system runs out of space.  Upon removing the files & rebooting, the files start being generated again.

I’ve found that this is caused by large Component-Based Servicing logs.  These are stored at C:\Windows\Logs\CBS.  The current log file is named “cbs.log”.  When “cbs.log” reaches a certain size, a cleanup process renames the log to “CbsPersist_YYYYMMDDHHMMSS.log” and then attempts to compress it into a .cab file.

However, when the cbs.log reaches a size of 2 GB before that cleanup process compresses it, the file is too large to be handled by the makecab.exe utility.  The log file is renamed to CbsPersist_date_time.log, but when the makecab process attempts to compress it the process fails (but only after consuming some 100 MB under \Windows\Temp).  After this, the cleanup process runs repeatedly (approx every 20 minutes in my experience).  The process fails every time, and also consumes a new ~ 100 MB in \Windows\Temp before dying.  This is repeated until the system runs out of drive space.

The Cause

When the system works correctly, the integrated CAB compression unit should compress the Trusted Installer CBS log before it reaches 2 GB. Unfortunately, the CAB cannot handle files larger than 2 GB and starts having a jolly bad time. As a result, the CAB compressor (makecab.exe) generates a huge amount of useless and massively bloated TEMP files Keep Log & Temp Files Under Control With This Windows Script I've spent a lot of time helping out friends and family with their computer issues, and I have to say that above all other problems, the one issue that I see come up again and... Read More , which will rapidly fill any hard drive.

It’s unclear why the log file is permitted to grow larger than 2 GB. Logging might happen too fast for the compression to keep up and the culprit here could be Windows Update This Is Why We Hate Windows Update The way Windows Update currently forces Windows 10 upgrades and updates on you is bad. Gavin examines what makes all of us hate Windows Update and what you can do against it. Read More . Once a log file has grown to 2 GB or more, it causes the compression tool to crash and enter a vicious circle, accumulating temporary junk files until the drive is full.


This bug is irritating and time-consuming, to say the least. And why Microsoft continues to eschew better compression tools is beyond me.

The Manual Fix

Woody Leonhard, of Woody on Windows over at InfoWorld, has detailed how to manually fix this issue. Jump below the tweet to see how you can release yourself from this turmoil.

Press Windows key + R to open the Run dialog. Type services.msc to open the local services panel How To Control Running Services With The SC Command [Windows] One of the things that I find myself doing much more often since diving into IT is monitoring and checking the status of services running on computers that are running across the company. There is... Read More .


Browse to down to the Windows Modules Installer and turn it off.

Windows Module Installer Service

Now head to %rootdirectory% > Windows > Logs > CBS.

You’ll now need to move or rename each of the files in the directory. Depending on how many files are present, it may well be easier to move them all to a different directory.


CBS Files in Folder

Now head to %rootdirectory% > Windows > Temp.

In the top-right corner, enter cab* and search. If there are any results, delete them.

CAB Search Bar in File Explorer


Reboot your system.

You should now find your Windows Module Installer service up and running like normal, and makecab.exe should be able to actually process the files, rather than repeatedly throwing up all over your hard drive.

Clean Your Windows Caches

If you’re running Windows 10 and have noticed your precious hard drive numbers slowly dropping, it could be one of the numerous caches accumulating data without you realizing.

We previously detailed how to go about finding and clearing each of the following caches 7 Hidden Windows Caches & How to Clear Them Cached files can take up a lot of bytes. While dedicated tools can help you free up disk space, they might not clear it all. We show you how to manually release storage space. Read More , but I’ll list them just so you’re aware:

  1. Windows 10 Update cache
  2. Windows Store cache
  3. Temp Files cache
  4. Thumbnail cache
  5. System Restore cache
  6. Web Browser cache
  7. DNS cache

While clearing your DNS cache is really not going to grant you anything like the space clearing your Temp Files cache might, we also have some effective suggestions for how to free up some space Low Disk Space? 5 Native Windows Tools To Free Up Storage Space Don't download a fishy third party tool to reclaim valuable disk space! Windows has its own tools for the job and they're easy to use. Read More .

Bug Free Existence

You should now have control of your hard drive once more, free from the grips of the errant makecab.exe, and able to actually delete the offending files with spawning a billion more (trust me, I counted them).

How do you keep your system size down? Regularly empty your downloads folder? Delete anything other than what is necessary? Let us know your techniques below!

Related topics: Windows 10, Windows 7, Windows 8, Windows 8.1.

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  1. David Brumley
    September 12, 2016 at 3:19 pm

    Would Piriform's CCleaner handle the clean-up of the various caches as mentioned above?
    If not, is there another tool that would work? Thanks for this interesting information. I am running Win7, and have not (yet) experienced this disappearance of HD space.

    • Kelsey Tidwell
      October 2, 2016 at 2:08 am

      CCleaner will do this if configured appropriately. I've used it before and like it, but for the last couple years I've used Iobit's Advanced Systemcare9 which also incorporates many more system optimization features.