By default Windows will “hide extension for known file types”. A filename extension is a suffix that indicates the file format like .jpg or .txt. This setting is exploited to distribute malware in seemingly innocent files, for example via emails. A file that appears as “image.jpg” could in reality be “image.jpg.exe”, an executable file that installs a piece of malware on your PC once opened. The default Windows setting would make the real file extension “.exe” disappear.
Cybercriminals also use utilize this method to distribute ransomware, which encrypts personal files and threatens to delete them unless a certain ransom is paid. The emergence of Bitcoin has made caused an increase in this type of malware, as Bitcoin payments can be demanded on anonymous addresses. One of the ways that can help to counter the distribution of this malware is simply unhiding file extensions. This can be done in the Control Panel under “Folder Options”.