Virus, malware, ransomware, trojans and any other kind of dangerous code often travel through emails. We also receive dozens of spam messages every day via e-mail, mostly containing unwanted advertising. Sometimes, however, they also contain attached files that can hide a danger.
According to the well-known antivirus manufacturer Kaspersky, for example, there are four types of files that are frequently used by those who want to attach a virus to an email message. From the most frequent to the least frequent, these file types are: compressed folders in ZIP and RAR format, Microsoft Office documents (especially .DOC and .DOCX), PDFs and ISO and IMG images. Infections based on these types of attachments are the order of the day and each of these files has been used in the last year to launch different types of hacker attacks and spread viruses, more or less dangerous.
ZIP and .RAR attachments
The .ZIP and .RAR files have a great advantage: being complex archives, they can contain dangerous files inside them without them being recognized from the outside. In other words, until we unzip the compressed file we can’t know what it contains. On the eve of Valentine’s Day, for example, a ransomware campaign was launched based on attachments with filename “Love_You” + a number and .ZIP extension. Once the file was opened, the user’s PC was locked and a ransom demand was displayed on the screen.
File attachments .DOCX, .XLSX, PPTX
The files of the Microsoft Office personal productivity suite are only apparently harmless: they may contain macros, i.e. small programs that are executed when the file is opened. These macros can contain viruses, as recently happened in Italy with the banking trojan Ursnif.
PDF attachments
The .PDF is another file format that is very popular online and, therefore, is one of the most used to spread malicious code. Also because it can contain JavaScript code to perform certain functions. Therefore, just like macros in Office files, scripts inside .PDF files can also infect our PC or mobile devices.
Iso and .IMG files
The .ISO and .IMG file formats are the ones normally used to copy CDs, DVDs and other types of discs. In jargon, they are called “images”, even though they do not contain photos or drawings. However, the same applies to them as to .ZIP and .RAR files: they can contain infected files and once you open the image, these files can run and damage your PC.