Data exhaust refers to the trail of data left by the activities of an Internet user during his/her online activity. An enormous amount of often raw data are created. These data (which can take the form of cookies, temporary files, logfiles etc.) can help to improve the online experience (for example through customized content). But they can also compromise privacy, as they offer a valuable insight into the user’s habits. It can be used to improve tracking trends and studying data exhaust also improves the user interface and the layout design.
Unlike primary content, these data are not purposefully created by the user, who is often unaware of their very existence. A bank for example would consider as primary data information concerning the sums and parties of a transaction, whilst secondary data might include the percentage of transactions carried out at a cash machine instead of a real bank.