It is difficult to find an email user who has never received any kind of spam. Some get mail from dubious correspondents in their inboxes from time to time, and others have to purge hundreds of those messages every day. Mass mailing is a serious problem not just because it consumes time and physical resources for the process of sorting emails, but also because they are a frequent source of malicious content. One infamous example of cyberweapons – Duqu Trojan – infects systems after an apparently harmless text document has been opened, thereby exploiting a vulnerable system. Moreover, attackers actively use the so-called spearphishing method (targeted mailing with a fake sender’s address to a specific list of email addresses) to penetrate the targeted organization’s infrastructure. This sort of an attack was implemented in the APT “Hellsing“, when cybercriminals delivered malware via targeted emails with attachments.