When you install a major Windows 10 update, you may reboot to find some of your programs missing. Yes, Windows 10 may remove your programs without asking you–but you can get them back pretty easily.

This is the takeaway from some people’s experiences with the “November update,” Windows 10’s first big update. Microsoft has refused to comment on this, but it seems like the update process is designed to remove incompatible programs. Here’s what’s going on, and what you can do about it.

Windows Only Does This During Major Updates

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To start: Windows won’t just remove programs at random times. It will only remove programs when updating to a new major version, or “build,” of Windows 10.That’s because these major versions, or “builds,” are treated differently from normal Windows updates. Builds of Windows 10–like the fall update, Windows 10’s first big update–aren’t like normal Windows updates or service packs at all. Instead, they’re more like upgrading to an entirely new version of Windows.

As part of the upgrade process, Windows leaves your old Windows installation–or old Windows build–files in the “Windows.old” directory on your system drive. That’s usually C:\Windows.old . This is also displayed as “Previous Windows installation(s)” in the Disk Cleanup application.

Why Windows Decides to Remove Programs

Windows may remove programs during an update for compatibility reasons. If a program is known to cause crashes, bugs, or otherwise conflict with Windows, Windows may remove it to keep your system stable. If this happens, the “All of your files are exactly where you left them” screen will appear like normal–this screen always appears during major updates–but Windows will actually have removed some of your program files.

It looks like this feature is designed to help protect the average Windows user, who might have outdated programs installed. Windows can clean them up and make sure they don’t cause problems. However, Windows doesn’t provide any notice that it’s removed a program–the program will just appear to vanish from your system.

When Windows 10’s first big update arrived, many people on Reddit noticed a variety of programs were being silently removed–most of which were hardware-related utilities. People have reported that it removed the popular Speccy, CPU-Z, HWMonitor, and CCleaner programs from many people’s systems. Many people claim it removed hardware drivers like Intel Rapid Storage Technology and AMD Catalyst Control Center, too. In some cases, people even reported that it removed PDF viewers and antivirus programs (perhaps outdated ones). Confusingly, it seems like the Windows update removed these programs from some computers but not others. Reports are not completely consistent.

Microsoft hasn’t directly commented on this. In fact, Microsoft specifically declined to comment when asked about this by VentureBeat. We also haven’t seen them issue a statement to any other media outlet or a blog post on the subject. That’s why we can only piece this together from what people are reporting on social media and forums. However, the Microsoft Services Agreement that applies to Windows does explicitly state that Microsoft may remove access to software or hardware.

The Fix: Just Reinstall the Program

If you run into this problem and you want to get the program back, just reinstall it. In most cases, this will involve re-downloading the program from its developer’s website. You’ll probably be downloading a newer version of the program than the one that Windows uninstalled, so it may just work without any hassle.

However, even if the latest version a program conflicts with Windows, you’ll be able to reinstall it. You may need to reinstall it again after the next major update to Windows 10, if Microsoft decides to keep removing programs during upgrades.

If the program really is incompatible with modern versions of Windows–for example, if it’s an antivirus program that’s several years old–you should probably take the hint and switch to a more modern program, if you can. But Windows seems to be removing programs that work perfectly fine and Microsoft hasn’t issued a statement about how this works.

How to Recover the Program’s Files

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Windows shouldn’t remove any important files, but it may accidentally remove settings or other files associated with a program. (We’re really not sure about this, as Microsoft won’t explain how this works.)

If you need the program’s files back, you can get them. Windows 10 will keep your old Windows files for 30 days after an upgrade, storing them in the C:\Windows.old folder. This allows you to roll back to the previous build of Windows 10 if you have a problem.

However, if you’ve removed old Windows installations using Disk Cleanup or manually deleted the Windows.old folder after the upgrade, it won’t be there. Otherwise, assuming it’s been less than 30 days, your old program files will still be there for you to recover.

To find them, open File Explorer and navigate to the C:\Windows.old folder. You’ll see the directory structure of your old Windows installation. For example, if the program was installed in C:\Program Files (x86) , you’ll find its files in C:\Windows.old\Program Files (x86) . If Windows removes a program’s application data, you may find it somewhere under C:\Windows.old\Users\NAME\AppData , depending on where Windows stores the data.

You can’t necessarily just copy a program’s files to your current Windows installation, as any registry entries the program depends on may be gone. You’re better off reinstalling it. However, this trick will allow you to recover any files Windows removes. Windows won’t immediately delete them.

We didn’t actually run into this issue with the November update ourselves, but we’ve seen many reports of it and know people who have. Unless Microsoft changes its mind, Windows 10’s big updates will continue to automatically uninstall various programs without any notice in the future. Microsoft should be a bit more transparent about this, explaining when Windows does this and telling users when programs have been uninstalled.