The most dangerous application of this naming convention occurs when attackers hide executable files behind harmless media extensions.
Every file on your computer has a file extension—a suffix consisting of a period followed by a few letters (like .jpg , .pdf , or .mp4 ). This extension tells your operating system which program should be used to open the file. JULIE.mp4.mkv.mp4
Because Windows might hide the .exe extension, the user only sees GreatVideo.mp4 . The most dangerous application of this naming convention
Automated file rippers, conversion scripts, or peer-to-peer file sharing networks sometimes glitch and append duplicate extensions during automated processing cycles. JULIE.mp4.mkv.mp4
An attacker creates a malicious executable script and names it GreatVideo.mp4.exe .