Some people argue that by leaving their WiFi networking open for anyone to use that they are promoting sharing. They deliberately allow others to use thir WiFi to connect to the internet because they think nothing of using other's WiFi to connect when they are away from home. I suspect that this group actually make up only a minority of those who have left their WiFi open so that anyone can use it. By far the majority of people who have left their WiFi open will have done so simply because they didn't bother to read the manual so as to learn how to close it.
Regardless of why people have left their WiFi open, there are issues with open WiFi that they almost certainly have not considered since if you look at all of the issues relating to open WiFi you would most definitely make the effort to close it.
One issue that came up with regard to open WiFi was when Google sent their trucks around all the streets in various cities to get photos of everything from street level. When they did so they also collected signals being transmitted from all the local WiFi networks as they passed them. In the case of all the open networks this collected information consisted of plain text and contained all sorts of information that was being transferred at the time the truck passed and probably included the login details for many people's accounts on a variety of web sites. In the case of closed WiFi networks all the data being transferred is encrypted and so beyond knowing that a WiFi network existed, they would have obtained no useful information whatever.
Another far more common and ongoing issue with open WiFi is that anyone within range of the WiFi access point can connect to the network and has as much access to the other devices on the local network as anyone else on the local network does. If your WiFi network has several computers with file sharing enabled to allow you to share files between thosde computers then anyone who connects to your WiFi also has access to all those same files.Sites providing a public open WiFi network are very careful to ensure that their own local network is kept completely separate from the one that provides the open WiFi so that there are no shared files on their system accessible via the WiFi. They leave it for each person using their WiFi to ensure that they don't have file sharing enabled on their computer so as to not share their files with other people sharing the public WiFi access.
A more obvious way in which an open WiFi can be used/misused is that it provides anyone who can connect to it with internet access. Now those who deliberately leave their WiFi open do so for this specific purpose but have probably overlooked all of the other issues. They have also overlooked the ways in which the internet access can be misused. In the case of those who left their WiFi open through ignorance, they may find that the limited internet access they pay for is used up far more quickly than they expected due to others using their connection without them knowing. A bigger issue though is that you have no control over what those other people are downloading using your internet connection. There have been instances where people have been arrested and all their computers seized because their internet connection has been used to download illegal material. They get released eventually once it is proved that they weren't the ones who used their connection to do the downloads but it could be argued that they assisted in the download of the illegal material by making their internet connection available.
Closing your WiFi so that only those computers you want to have access can do so is relatively simple and will just require that the password for the connection be entered once into each of the computers after the access point itself has been configured. A few minutes to configure your WiFi to close it to all except your own computers will save you from the many issues that open WiFi presents.
This article written by Stephen Chapman, Felgall Pty Ltd.