Taken from the official Shannon Airport website;
Shannon Airport currently has FREE public wireless (WiFi) broadband internet access available throughout the terminal.
Support for this service is provided by Shannon Airport Information Technology and Telecommunications (IT&T). The system is easy to use, and requires a simple registration process. Authenticated users are permitted a generous 5 hours usage per day and 100MB* data throughput.
Shannon Airport IT&T will be happy to assist users should they have any difficulty connecting to the Wi-Fi network. A Wi-Fi connect guide is available at the information desk in the arrivals hall and at various locations throughout the terminal. The Wi-Fi service is provided "as is".
Users will require their own WiFi enabled computer equipment and should have "administrator" rights on their computer to access the WiFi network. The WiFi network should be considered as unsecured and users are responsible for their own protection measures e.g. firewall, anti-virus and anti-"spyware".
The Hughes & Hughes bookstore in the arrivals area provides coin operated and/or credit card access to the internet. This is available 24 hours a day, 365 days a year. Users may access this service using either the dedicated computer equipment or by connecting their own laptops to the Hughes & Hughes dedicated broadband connection.
Official Website: http://www.shannonairport.com/facilities/internetaccess.html