Symantec has reported an increase respect last year result of a surge in polymorphic malware attacks, particularly from those found in Web attack kits and socially engineered attacks using email-borne malware. The malware diffusion during last year is rapidly increased due to the growth of Drive-by attacks against internet users. The infection process is subtle but effective, it is sufficient that users visit a compromised website. Another factor that has dramatically impacted on the malware diffusion is the availability in internet of exploit toolkits.”]
Source: http://securityaffairs.co/wordpress/6491/cyber-crime/the-malware-factory.html