  Anonymity networks are becoming increasingly popular in today's online world
as more users attempt to safeguard their online privacy. Tor is currently the
most popular anonymity network in use and provides anonymity to both users and
services (hidden services). However, the anonymity provided by Tor is also
being misused in various ways. Hosting illegal sites for selling drugs, hosting
command and control servers for botnets, and distributing censored content are
but a few such examples. As a result, various parties, including governments
and law enforcement agencies, are interested in attacks that assist in
de-anonymising the Tor network, disrupting its operations, and bypassing its
censorship circumvention mechanisms. In this survey paper, we review known Tor
attacks and identify current techniques for the de-anonymisation of Tor users
and hidden services. We discuss these techniques and analyse the practicality
of their execution method. We conclude by discussing improvements to the Tor
framework that help prevent the surveyed de-anonymisation attacks.
