Virus Affecting Storage Space?

Question

I continuously get a notice that my storage space is running low. I'll delete 10+ gigabytes and the immediate effect is that Windows shows the additional storage. But overnight, all that storage disappears and I get a low storage warning.

I've looked for a large folder that my have unneeded files. The Windows folder shows over 70 gigs of storage. When I look at individual folders, I'll find one showing a bit less than 70 gigs, but when I go into it, I cannot find files of that size. When I come out of the folder, it shows it's real storage size, and another folder will show the 70 gigs.

This acts like some sort of virus. But a Norton deep scan did not affect it.

Answer 1

Most likely, this is not a virus, it may be some windows process causing the problem, the Windows folder should never be that size,

Download the free TreeSize app from the Microsoft Store.

Very Important - to run TreeSize, you must right click its icon and choose Run as Administrator.

1

Please provide a screenshot of your C drive in that TreeSize utility, so I can see your hard drive and work out where that space is being used and if there is an underlying problem.

2

Also, please provide another screenshot of the TreeSize app window after you expand the Windows folder in the app.

Please ensure the full TreeSize window is in the screenshot, there is information on the top and bottom bars I needs to see.

Answer 2

The described behavior is consistent with normal Windows disk usage patterns (temporary files, update files, Store cache, etc.) and low‑space conditions, not necessarily with an active virus, especially if reputable antivirus scans are clean. Focus should be on identifying and cleaning up system‑generated files and configuring Windows to manage space automatically.

Try the following steps on Windows 11:

1. Check what is using the space
2. Open Settings > System > Storage.
3. Let the storage analysis complete and review which categories (e.g., Temporary files, Apps & features, System & reserved) are consuming the most space.
4. Use Cleanup recommendations in Storage to identify and delete temporary files, large or unused files, files already synced to the cloud, and unused apps.
5. Turn on Storage Sense for automatic cleanup
6. Go to Start > Settings > System > Storage.
7. Turn on Storage Sense to automatically free up space by removing unnecessary files (temporary files, Recycle Bin contents, etc.).
8. Configure it to run automatically when disk space is low.
9. Clear Microsoft Store cache if temp files keep growing If free space disappears again quickly, the Temp folder may be filling with Microsoft Store (.appx) files.
10. Press Windows key + R, type wsreset.exe, and select OK to clear the Microsoft Store cache.
11. After the blank Command Prompt closes and Store opens, restart the PC.
12. Move personal files off the system drive To prevent the system drive from filling up again:
13. Connect an external drive or ensure a secondary internal drive is available.
14. Move large personal files (videos, music, photos, documents) from the system drive to that other drive.
15. Configure Windows to save new content to another drive:
    • Start > Settings > System > Storage > Advanced storage settings > Where new content is saved.
    • For each content type (documents, music, photos, videos, etc.), select a different drive from the drop‑down.
16. Use OneDrive Files On‑Demand (if using OneDrive) If OneDrive is in use, enable Files On‑Demand so that only placeholder files are stored locally and full files stay in the cloud. This can reclaim significant space if many files are synced.
17. Run an additional malware check with Windows Security Even though Norton found nothing, run a scan with Windows Security as well, to double‑check for malware that might be generating files:

• Open Windows Security and run a full scan. If anything is found, follow the cleanup recommendations.

If, after these steps, free space still drops by many gigabytes overnight and Storage settings do not show where it is going, consider backing up important data and using Reset this PC (Keep my files) as a last resort to repair system corruption while preserving personal files.

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References:

• Free up drive space in Windows
• Fix low disk space errors quickly in Windows
• Windows 10 update issues on devices with low storage space