The most generally used and shared file types have accounted for 70% of spear phishing email attachments.
Nearly 91% of the targeted attacks begin with a spear phishing email, according to a new report from Trend Micro.
According to the report, 'Spear Phishing Email: Most Favored APT Attack Bait,' 94% of targeted emails involve malicious file attachments as the infection source, with the remaining 6% involving other methods that advice user to install malware via malicious links.
Trend Micro security research and communications director Rik Ferguson said that the firm expects to see a resurgence of malicious email as targeted attacks expand and evolve.
"Experience has shown us that criminals continue to abuse tried and trusted methods to directly leverage intelligence gathered during the reconnaissance for targeted attacks," Ferguson said.
"We have also seen that targeted attacks are evolving and expanding.
"The abundance of information on individuals and companies makes the job of creating extremely credible emails far too simple. It's a part of a custom defence that should not be ignored."
During period of Trend's study between February and September 2012, the most generally used and shared file types have accounted for 70% of spear phishing email attachments.
The main file types include .RTF, .XLS and .ZIP, while Executable (.EXE) files were not highly used as emails with .EXE file attachments could be detected and blocked by security products.