Your 'Unique Plugin Installation ID' is an automatically generated ID for this plugin on your particular site.
- It doesn't contain or embed any identifiable information about you or your site
- It is an MD5 hash of some random data which was generated when your plugin was installed / updated from v4.15.0+
- It is to be used for certain functions which will grow as the plugin develops. e.g. forceoff
To see your installation ID, go to the Shield plugin Dashboard => General Options => Installation ID. (See the screenshot below)