Sophos’s “Evolution of Network Security” graphic tracks both the threats and the thwarts (countermeasures), beginning with the worldwide infection of the “I love you” worm. The point, of course, is to sell you on the UTM as a solution, but you’ll find the timeline interesting.
http://www.sophos.com/en-us/security-news-trends/security-trends/network-security-evolution.aspx