http://www2.dcsec.uni-hannover.de/files/android/p50-fahl.pdf
https://www.dfn-cert.de/dokumente/workshop/2013/FolienSmith.pdf
https://resources.sei.cmu.edu/asset_files/Presentation/2015_017_101_442549.pdf
http://stackoverflow.com/questions/5909/get-size-of-a-file-before-downloading-in-python