@inproceedings{polakis:acsac13, <br>
author    = {Iasonas Polakis and
Stamatis Volanis and
Elias Athanasopoulos and
Evangelos P. Markatos},<br>
title     = {The man who {\it was} there: validating check-ins in location-based services}, <br>
booktitle = {Annual Computer Security Applications Conference (ACSAC '13)}, <br>
year      = {2013},<br>
pages     = {19-28},<br>
}