A CHM file (Compiled HTML Help file) is a Microsoft proprietary format used to deliver online help documentation in Windows applications. CHM files contain a collection of HTML pages, images, and scripts, all compressed into a single file. While originally intended for legitimate help content, CHM files can be exploited by cybercriminals to deliver malware. This is because they support embedded scripts and objects, which can be used to execute malicious code when the file is opened. Attackers often distribute malicious CHM files via email attachments or downloads, tricking users into opening them and inadvertently compromising their systems. Security best practices recommend caution when handling CHM files from unknown sources.