The growing disquiet about how companies track our every move on the web.
Whenever you go online you leave footprints everywhere, recording where you have been and what you have been doing. This is all gathered and recorded by special software, deployed by everyone from advertising firms to social networks.
There is an increasing number of people now calling for the practice to be regulated. But, as Ian Hardy reports, stopping websites from using tracking software could have a high price for users themselves.