  Speech technology for communication, accessing information and services has
rapidly improved in quality. It is convenient and appealing because speech is
the primary mode of communication for humans. Such technology however also
presents proven threats to privacy. Speech is a tool for communication and it
will thus inherently contain private information. Importantly, it however also
contains a wealth of side information, such as information related to health,
emotions, affiliations, and relationships, all of which are private. Exposing
such private information can lead to serious threats such as price gouging,
harassment, extortion, and stalking. This paper is a tutorial on privacy issues
related to speech technology, modeling their threats, approaches for protecting
users' privacy, measuring the performance of privacy-protecting methods,
perception of privacy as well as societal and legal consequences. In addition
to a tutorial overview, it also presents lines for further development where
improvements are most urgently needed.
