A Spanish start-up called Fon has attracted a $21.5m investment from investors including Skype and Google to build a global shared Wi-Fi internet access infrastructure. 

Fon aims to build a service based on consumers sharing their broadband internet access with other individuals.

Users are required to download a special application to run on their Wi-Fi routers, or purchase a router with the software pre-installed. The application only supports Linksys WRT54GL, WRT54GS and WRT54G routers, but more will be added in the future.

The firmware upgrade creates a second separate network that operates independently from the user's home network to prevent any security breaches. The shared network is configured to use no more than 50 per cent of a user's bandwidth.

The service defines three kinds of users. Non-members who pay to get access to the network are called 'Aliens'. They use the network of 'Bills', people who provide internet access at a fee. A 'Linus' is a user who shares the connection free of charge with other members.

Sharing a broadband internet connection in some cases violates the terms of use, but Fon hopes to gain support from providers through revenue sharing deals.

Martin Varsavsky, the firm's founder, admitted that the service will initially have little appeal, but should get more interesting as more users sign up.

"At the very beginning, when there are no obvious advantages to joining Fon, it is not so easy to get Foneros [users], even though the service is free," he wrote on his blog. 

"But as Foneros continue to join, and there are more and more Fonero hotspots, the dream of a unified global broadband wireless signal becomes a reality.

"The Fon movement, as we call it, can achieve what 3G or EVDO has not: a truly broadband wireless internet everywhere. 3G/EVDO are great for coverage, but their throughput is pitiful compared to Wi-Fi and they are way too expensive."

The service has been live in Spain and the US for about 90 days and claims over 3,000 registered access points. An overview of access points mapped out on Google Maps is available here. 

The company's website also lists team members in Argentina, France, Germany, Ireland, Israel, Japan, Mexico and Sweden.