@fry_p You can change both, line 110 and 114. If all works fine, when you are in FOS, must return 111 code. If you are under windows, must return 0.
which value return when you are under windows? 0 or 6?
If the value is 6, which OS are you using (Windows 7,8,10)?
Another oddity is that the built in host pinging on the host list page is working properly and even detecting these are windows clients.
The hostStatus plugin uses the same code that FOGHostPing daemon, if the daemon detects fine the status, there is something that doesn´t work correctly.
You have 1500 hosts, the daemon launchs one ping per second then the status is updated every 25 minutes, in your case the status info is not very reliable. In my opinion is better disable this daemon.