A macro is a compact set of commands or instructions for performing a task. While macros are often used legitimately to automate helpful actions, they can also be used by attackers to automate harmful ones.
In this case, the document file itself is essentially bait, carefully designed by attackers to lure recipients into opening it and launching the harmful macro code.
Distributing the document files
The most common method attackers use to spread their specially-crafted document files is as attachments to spam email messages.
In attacks that are targeted at specific organizations or persons (also known as spear phishing), the email messages are deliberately tailored to its audience, to increase the chances that the recipients will accept the attached document as authentic and open it.
Tricking the user
The bait files are typically configured so that the macro will automatically run when the document is opened. However, the latest versions of Word software will by default block Word files that were downloaded from the Internet from automatically running macros.
To bypass this security precaution, if the macro cannot automatically launch, the document file displays a notification message asking the user to "allow a macro to run".
If the user clicks 'OK' on the notification message, the macro is launched. If the user does not click 'OK' and closes the file, the macro cannot run.
Once the macro runs, it can perform a number of harmful actions. The specific action taken can vary, but the most common ones are:
- Contacting a remote site to retrieve additional instructions
- Downloading and/or installing additional files
- Harvesting confidential information from the device
- Transmitting stolen data to a remote site