“…Spam is the most common method of virus infiltration [62] and accounted for about 80% of the 182.9 billion e-mails sent and received per day in 2013. Spam consumes resources (time spent reading messages, bandwidth, CPU time and disk memory), but is also used to spread malicious content such as online fraud or viruses [63,64]. According to a recent study by the Radicati Group, the amount of spam received between 2013 and 2017 is expected to remain at roughly 15% of the e-mails received, thanks to anti-spam technology [65].…”