\chapter{Introduction}
\label{chap:introduction}

The Internet has seen an unprecedented rise in traffic over the last few years
which is accelerating still. Due to this growth, an increasing amount of user
data is sent over the Internet. This user data is analyzed by companies in big
industries such as social networking, advertising, internet service providers
and news web sites. Although many services online appear to be free for
individual users, the companies behind them have to sustain themselves and make
profits every year. This has led to firms working extensively with user data to
extract meaningful information from the way users use their services. The
collected and inferred information can then be sold to interested parties which
allows those parties to personalize their service, yielding higher customer
engagement and thus higher profits. The end users themselves receive the short
end of the stick by---often unconsciously---giving away their data without
gaining much in turn. Because the means of data collection on the Internet are
becoming increasingly invasive and omnipresent, tools to defend against such
privacy intrusions are developed. It is beneficial to users to know how web
sites are tracking their customers so that they can protect themselves against
these tracking mechanisms. The aim of this thesis is to give an overview of
tracking methods and tools to defend oneself against them. It seeks to answer
the underlying research question of \emph{Which stateful tracking methods are
used to track individuals on the Internet and which countermeasures exist?}

\section{Terms and Scope}
\label{sec:terms and scope}


