Use a more straightforward return style in script rules. Instead of

if cond then
		return true
	else
		return false
	end

just do

	return cond

scripts/smb-security-mode.nse

@@ -60,15 +60,7 @@ require 'smb'
 
 -- Check whether or not this script should be run.
 hostrule = function(host)
-
-	local port = smb.get_port(host)
-
-	if(port == nil) then
-		return false
-	else
-		return true
-	end
-
+	return smb.get_port(host) ~= nil
 end