W97M

The Microsoft Office productivity software suite is one of the most commonly found set of programs on computers around in the world, on both business and personal computers. The suite includes the Word, Excel, Powerpoint, Outlook, OneNote and Access programs, as well as other less commonly used software.

Exploiting the user's trust

Because Microsoft Office is so commonly used, most computer users are familiar with it and generally trust files associated with its programs. Attackers thus try to exploit the implicit trust and familiarity users have with such files by secretly embedding malicious code into document files and distributing them, either en mass or to targeted users.

These 'bait' files are often specifically designed, or 'socially engineered', to look legitimate. For example, they may use filenames such as 'resume.doc' or 'invoice.docx', and contain content (sometimes stolen from actual legitimate documents) that seem authentic. The careful crafting of the bait files is meant to encourage the user to believe the document is trustworthy and open the file - and in so doing, unsuspectingly run the malware.

Macros, downloaders and droppers

Some W97M malware exploit vulnerabilities in the Microsoft Word program itself to execute code on the user's computer, though this is relatively less common, since it requires more technical skill to accomplish. Other W97M malware are independent programs that only use the Word document as a 'carrrier', and once run they can operate separately. One example of this type of malware is Trojan:W97M/Streedom.A.

The most common type of W97M malware however is a malicious macro embedded into the Word document itself. A macro is a tiny program that can be legitimately used in Word to automate some functions, but an attacker can also craft a macro to perform malicious actions. Most often, these malicious macros are used by attackers to download additional malware onto the user's computer. Some representative examples of macro malware in Word documents are:

• W97M.Downloader.QK
• Trojan-Dropper:W97M/Kukudro.A
• Virus:W97M/Argh
• Virus:W97M/Walker

Note

With changes in the threat landscape today, F-Secure has updated its platform designation convention and malware affecting this platform now uses the platform designation, 'WM'.