There are a zillion (or possibly more) Facebook games all with those little publish boxes that post to your wall or your friends walls... When you get one of those publish pop ups, there is a drop down box directly to the right of the "Publish" button. From there you can select:
Everyone, Friends Of Friends, Friends, or Custom.
Everyone is the default, so unless you want game bots picking up your bonuses or total strangers trying to add you as a friend because they want game neighbours, change that to Friends Only. If you have a bonus that you want to go to special friends, use the Custom feature to select them. That way only your selected friends will be able to pick it up.
