“…Difficulty [Byres et al, 2004, Fung et al, 2005, Tanu and Arreymbi, 2010, Henniger et al, 2009, Amenaza, 2001, Mauw and Oostdijk, 2005, Abdulla et al, 2010, Amoroso, 1994, Wang et al, 2011 The technical or social skill level needed for the attacker or defender to succeed.…”