Is this filevault something you wanted installed?
Is your iMac a home computer? If so is it behind a router. If it is you don't need the StatefulFirewall. The router will be plenty secure enough.
Do you have a current Time Machine backup of your boot drive?
Is this StatefulFirewall something you want installed? If not then I'd force shutdown your iMac by holding down the Power button until it shuts down.
Next, boot up into Safe Mode according to How to use safe mode on your Mac.
Note: if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode. This makes it act as a wired keyboard as will assure a successful boot into Safe Mode.
Finally, download and run the shareware app Find Any File to search for any files with the application's or the developer's name in the file name. For StatefulFirewall
software you'd do the following search(es):
1 - Name contains statefulfirewall
Any files that are found can be dragged from the search results window to the Desktop or Trash bin in the Dock for deletion.
FAF can search areas that Spotlight can't like invisible folders, system folders and packages.
If Find Any File doesn't find any files then you may be getting a spam notification. Was the notification in the form of a rectangle in the upper right hand corner of your screen? If so try this:
