  The 2019 Coronavirus disease (COVID-19) pandemic, caused by a quick
dissemination of the Severe Acute Respiratory Syndrome Coronavirus 2
(SARS-CoV-2), has had a deep impact worldwide, both in terms of the loss of
human life and the economic and social disruption. The use of digital
technologies has been seen as an important effort to combat the pandemic and
one of such technologies is contact tracing applications. These applications
were successfully employed to face other infectious diseases, thus they have
been used during the current pandemic. However, the use of contact tracing
poses several privacy concerns since it is necessary to store and process data
which can lead to the user/device identification as well as location and
behavior tracking. These concerns are even more relevant when considering
nationwide implementations since they can lead to mass surveillance by
authoritarian governments. Despite the restrictions imposed by data protection
laws from several countries, there are still doubts on the preservation of the
privacy of the users. In this article, we analyze the privacy features in
national contact tracing COVID-19 applications considering their intrinsic
characteristics. As a case study, we discuss in more depth the Brazilian
COVID-19 application Coronav\'irus-SUS, since Brazil is one of the most
impacted countries by the current pandemic. Finally, as we believe contact
tracing will continue to be employed as part of the strategy for the current
and potential future pandemics, we present key research challenges.
