Apple has launched a global replacement programme for the first generation iPod nano due to the risk of the music player's battery overheating. On its official website's support page, the company said that in very rare cases, the battery in the music player may overheat and pose a safety risk. The affected iPod nanos were sold between September 2005 and December 2006. The affected first generation nano has a black or white plastic front and a silver metal back. Later models have a metal front and back. 'While the possibility of an incident is rare, the likelihood increases as the battery ages,' Apple said. Users are recommended to stop using the product and ask for a replacement unit free of charge. They should visit their nearest Apple Store or authorised service providers with their iPods. Customers from 20 countries, including the USA and Japan, can place their order for a replacement iPod on the web. But Hong Kong and mainland China are not covered by the online service.