Why @[4:0] will show Mark Zuckerberg’s name on Facebook
There is a well-known Facebook trick that will insert Mark Zuckerburg’s name, and tag him, anywhere on the website if you type @[4:0]. In fact, its not a trick at all, its a bug in the way Facebook tags users.
Facebook allows users to tag each other by starting a word with the @ symbol. However, when you type the @ symbol, you will be shown a list of names that you might be trying to tag. Each of these users will have a unique ID in the database. The fact that @[4:0] tags Mark Zuckerberg and links to his profile means that he is the 4th user in the database.
So who are the first three?
There isn’t any first three profiles. Visiting ‘https://www.facebook.com/profile.php?id=1’ will bring up an error. All three IDs will bring up an error, until you get to the 4th which displays Zuck’s profile.
Does that mean it will work for any profile?
Every single profile on Facebook is uniquely identified in the database by its numeric ID. You can find your Facebook ID with findmyfbid.com and do the same trick with your own profile, or any other profile on the website.
It didn’t work for me — has my Facebook been hacked?
I can across this picture on Facebook recently that stated if this trick didn’t work for you then your Facebook must have been hacked. To be honest, you have to be pretty special to believe this. If your Facebook had somehow been hacked, you’d know about it before you typed @[4:0]. How someone would come to that conclusion is beyond me. It doesn’t seem to work when you’re using the Facebook app, which may call data differently to the web application.
Update — February 2 2017
After some testing, it seems that this trick no longer works. Facebook may have patched the web application so tagging can no longer be done by calling a user’s ID. Inspecting the source of the tags shows no reference to the actual ID of the user tagged.