Alessio Conti Andrea Sterbini Marco Temperini IBS: Intrusion Block System a General Security Module for elearning Systems. 494-503 2011 DICTAP (2) http://dx.doi.org/10.1007/978-3-642-22027-2_41 conf/dictap/2011-2 db/conf/dictap/dictap2011-2.html#ContiST11