The average detection rate for these samples was 24.47 percent, while the median detection rate was just 19 percent. About two-thirds of the top email-based malware attacks in the past month have used exploit kits. Exploit kits are made to be sewn into the fabric of hacked or malicious sites, so that visiting Web browsers are checked for outdated plugins. When the malware slips past their antivirus, it is often just a question of whether the organization has someone or something in place that is vigilant about applying security updates.”]
Source: https://krebsonsecurity.com/2012/06/a-closer-look-recent-email-based-malware-attacks/