The version of ZoneAlarm you were running when you upgraded from Windows 7, 8.1, Vista to Windows 10 was not compatible with Windows 10. That's why after your Windows upgrade ZoneAlarm is gone but this can be easily fixed.
There is a new version of ZoneAlarm which is Windows 10 compatible and ready to be installed.
Windows 10 may already have our update ready to be installed.
To check go to the lower right corner of your screen and click on the Action Center icon
The Action Center will appear and if you see a section called Security and Maintenance notifying you that there is a new version of ZoneAlarm, Click on that message.
Your upgrade will begin and just follow all the prompts to install ZoneAlarm.
If you do not have the Above message you can still download and install a Win 10 compatible version.
Click the link below to download the latest version of ZoneAlarm.
Depending on what your default browser is you will see the installer download in that browser and this is how to run the installer.
Windows 10 Edge browser
In the bottom part of the browser you will see the installer downloaded.
After the download has finished click on the RUN button to begin the installation.
A download box will appear Click the Save File button.
When the download has completed Click on the downward pointing arrow at the top right area of Firefox
Then click on the installer file that was just downloaded to begin the installation.
In the bottom left area of the browser you will see the file being downloaded.
When the download has completed, click on installer icon to begin installation.