NBC to give away TV shows online

US TV network NBC is to offer free downloads of hit shows such as Heroes and The Office up to a week after they have aired on television.

The new service will launch in a test version in October before a full roll-out later in the year.

"Viewers want to be in control of how, when and where they consume their favourite entertainment," said vice president of NBC Digital Vivi Zigler.

NBC already sells episodes of some shows for permanent download.