The email messages used to deliver phishing-trojans are typically designed to look like normal business communications, often related to taxes, invoicing, deliveries, salaries or other work-related matters. They may also use the branding or names of legitimate companies to further the impression of authenticity. Such messages are also known as phishing emails.
The attached files are most often Microsoft Office documents (Word, Excel, etc), though PDF, HTML or ZIP files are also common. The files usually use innocuous file names, such as 'Invoice', or 'Delivery statement', to give the impression that they are legitimate.
The careful crafting of the email message and file attachments to appear authentic are all examples of social engineering.
Decoy documents and enabling macros
When the user opens the attached file, it will usually display an authentic-looking document as a decoy, to distract them from any unauthorized actions taking place in the background.
If the file is a Microsoft Office document file, and the user's Office program is set to disable macros by default, a notification message may be displayed asking them to enable macros, supposedly so that they can view the document properly. Instead, doing so allows harmful code secretly embedded in the document to run.
When the harmful code embedded in the file is run, it can:
- Drop a malicious component or program contained in the file onto the device and install it OR
- Contact a remote server and download a malicious component or program from the server onto the device
The specific harmful program installed onto the device varies, and may be separately detected by security products.