Antivirus without updating
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.
(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:\folder.
To find them, open File Explorer and navigate to the , depending on where Windows stores the data.
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.
In some cases, people even reported that it removed PDF viewers and antivirus programs (perhaps outdated ones). In fact, Microsoft specifically declined to comment when asked about this by Venture Beat.
Confusingly, it seems like the Windows update removed these programs from some computers but not others. We also haven’t seen them issue a statement to any other media outlet or a blog post on the subject.
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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. This is also displayed as “Previous Windows installation(s)” in the Disk Cleanup application.