Beware of "helpful" wall postings purporting to explain how you can protect your privacy, avoid scams, hackers, or viruses, or otherwise enhance your Facebook security. All too often the recommendations contained therein are wrong.
Consider, for example, the instructions below, which will supposedly cause all your comments and likes to be hidden from public view:
Hello to all of you who are on my list of contacts of Facebook. I would like to ask a favor of you…. You may not know that Facebook has changed its privacy configuration once again. Thanks to the new “Graphic app”, any person in Facebook anywhere in the world can see our photos, our “likes” and our “comments”. I am going to keep this message posted and I ask you to do the following and comment “DONE” if you like. Those of my friends who do not maintain my information in private will be eliminated from my list of friends, because I want the information I share with you, my friends, to remain among my friends and not be available to the whole world. I want to be able to publish photos of my friends and family without strangers being able to see them which is what happens now when you choose “like” or “comment”.
Unfortunately we cannot change this configuration because Facebook has made it like this. So, please, place your cursor over my photo that appears in this box (without clicking) and a window will open. Now move the cursor to the word “Friends”, again without clicking and then on “Settings”. Uncheck “Life Events” and “Comments and Like”. This way my activity with my family and friends will no longer be made public. Now, copy and paste this text on your own wall (do not “share” it!). Once I see it published on your page, I will un-check the same for you. Thanks so much!
It's an illusion. This option stops you seeing when other people have broadcast a message to a wide audience.
Please don't spread this advice, as it is confusing people and stopping the real problem from being fixed.
How to tell if a post will broadcast to all your friends:
Under each post (on the right) there is an icon which will tell you who it was shared with:
The globe icon means that the post is going to be public.
That means, if you comment your friends will be shown the comment immediately and that everyone on Facebook (except those people you have specifically blocked) can see it.
The icon showing two heads means that the post is shared with friends only.
It should be safe to comment, with no threat of exposure to strangers via the ticker/news feed.
A gear icon can actually mean one of two things - either Custom or Friends of Friends. You will have to hover your mouse over the icon to see which.
Custom means that the post will be safe to comment on with no leakage to strangers via the ticker/news feed.
Friends of Friends, however, can be considered unsafe - as all your friends and all of their friends will be shown the comment immediately via the ticker/news feed.
You can check your own posts easily that way if you want to make sure that your settings are right.