1. Information Security and Critical Infrastructure Protection Research Laboratory, Department of Informatics, Athens University of Economics & Business, Athens, Greece. E-mails: jsoup@aueb.gr, dgrit@aueb.gr
2. Joint Research Center, European Commission, Ispra Varese, Italy. E-mail: yannis.soupionis@jrc.ec.europa.eu
3. Department of Electrical and Computer Engineering, Democritus University of Thrace, Xanthi, Greece. E-mails: akoutsia@ee.duth.gr, pefraimi@ee.duth.gr