Ever noticed that airports all over the world have hotspots called "free public WiFi" that simply never work?
Unfortunately these hotspots are not real -- they are the result of a very poorly designed feature of Microsoft Windows XP.
When a Windows XP PC can't find any recognised Wi-Fi networks, it will automatically set up its own wireless hotspot (called an "ad hoc network") using the name of the last ad hoc network a user connected to.
Just about every laptop user gives "free public WiFi" at the airport a try at some point in the hope that it might actually be free Wi-Fi.
As a result, when their laptop doesn't find a recognised network at a future date, it broadcasts a "free public WiFi" hotspot.
The problem probably started when someone set up an adhoc network called "free public WiFi" as a joke -- and then the phenomenon started to spread to other people's computers due to the Windows XP "feature".
Generally, connecting to one of these "free public WiFi" hotspots won't do your computer any harm.
In most cases it'll just be someone's laptop announcing itself to the world, unbeknownst to its owner, and doing little else.
However, it is also equally possible that someone could sit in an airport deliberately running a "free public WiFi" hotspot, collecting email username and passwords. (That being said, there's nothing to stop someone sitting in the airport running a fake wireless hotspot called "Telstra", either.)
So there's one good rule of thumb: if you see a wireless hotspot called "free public WiFi", don't connect to it.
Laptops running newer versions of Windows such as Windows Vista or Windows 7 don't have this problem. Microsoft has even updated Windows XP to fix the issue in "service pack 3" -- but many people don't update their computers to the latest versions.
Unfortunately, despite being 10 year old software, Windows XP is still in common use on corporate laptops, so this problem persists around the world.