[en] In the last years, the paradigm of personal computing changed drastically, moving away from stationary PCs
and heavyweight laptops to mobile devices. This change is based on the ubiquity of mobile interconnected
devices leading to great opportunities for services that utilize location, such as navigation or communication
with nearby friends. Location-based Services (LBS) are widely used based on a centralized architecture and
absolute GPS positions. We focus on Proximity-based Services (PBS) based on peer-to-peer architecture to
detect what is around us. In addition, we provide further insights about which data are potentially useful to
create meaningful proximity information. Many LBS and PBS achieve their functionality without advanced privacy
protection mechanisms. However, mobile data especially location data is sensitive, because adversaries can
infer whereabouts of mobile users. Moreover, the uniqueness of human mobility traces is high yielding to a high
identification rate of individual users. Therefore, we review the most recent literature in the domain of private
proximity testing including attack models.