Many business owners want to offer free wifi access to their customers as an added courtesy/benefit. Few realise they could end up in court. Why?
As the owner of the network, you are held responsible for the activities on your network. (see http://www.ecrimewales.com/server.php?show=ConWebDoc.1140)
For example, if someone stays in your hotel and looks at child pornography, the police may well seize your computers and arrest you, unless you are able to prove it was one of your guests. The same would apply to hacking attempts using your connection, or people spamming emails from your wifi.
However, the most aggressive lawyers are from the music and movie industries, who routinely sue people for copyright infringements. In 2009, a pub owner was fined £8000 for filesharing
A very useful guide to using a wireless network in a business can be found at http://www.ecrimewales.com/server.php?show=nav.9315
To protect yourself or your business, you need to be able to prove the illegal activity was carried out by someone else. The only way to do this is to authenticate people logging on. You need a password, and only give this to those who complete a registration process. You also need proof of ID (e.g a car number plate, a credit card, or drivers licence.) The information needs to be recorded and produced in case of investigation. Passwords would need to be changed routinely also.
For most businesses, this overhead may be too cumbersome, so another approach is to use a service like The Cloud or BT Openzone. In these cases, the user has to sign up for the service with a card, who records their activities. It may not be as convenient as open wifi, but you can at least say you have acted responsibly.