Sky Broadband goes further than many broadband providers and hardware suppliers in supplying its Sky Broadband wireless router, a Netgear DG834GT, with wireless security switched on by default. This means the wireless network is secure out of the box, but it appears according to an article on The Register that if you can obtain the MAC address (a number which identifies individual pieces of networking hardware, and is nothing to do with broadband migrations in this case) the default security key can be worked out and someone could potentially use the connection.
The solution is for people to alter the security key, Sky Broadband has an article in its Help Centre which goes through the steps needed to change the security key. WPA-PSK Security Encryption is easier to configure as it will accept easy to remember phrases rather than complex hexadecimal strings like WEP, but be sure to pick a phrase that is not easy to guess, so for example avoid using your address, family names etc.
The chances of someone bothering to hack into your wireless network are probably slight and with the number of wireless networks that have no security enabled people are likely to look elsewhere. As was highlighted recently even using a wireless network without the owners permission is an offence that could lead to arrest. Hacking into a secured network no matter how easy it was to do will also be an offence.