More than three years after the infamous declaration from Microsoft's Bill Gates that "spam will be solved" in 2009, unsolicited junk mail continues to bombard email servers, dumping malicious attachments, phishing lures and spam advertising for fake pharmaceuticals. The success of these attacks forced email providers to block malicious attachments at the gateway level and, eventually, end users learned to avoid clicking on attachments. What followed was a classic cat-and-mouse game between attackers and defenders with hackers turning to legitimate file formats (PDF, JPG, MP3, etc.) to serve as the conduit for viruses, Trojans, rootkits and spyware.