OCX files are components used by Windows operating systems to provide reusable functionality to different software applications. They are essentially Dynamic Link Libraries (DLLs) with a specific structure and interface that allows them to be used as ActiveX controls. These controls can be embedded into various applications, such as Visual Basic, Microsoft Office applications (like Excel and Access), and web pages (using Internet Explorer). OCX files contain code, resources (like images and icons), and metadata that define the control's properties, methods, and events. They enable developers to create custom user interface elements and add specific functionalities to their applications without having to write the code from scratch. OCX controls were a popular way to extend the capabilities of Windows applications, allowing for code reuse and modular development. However, they are considered a legacy technology and have largely been superseded by newer technologies like .NET controls and other component-based architectures. Security vulnerabilities associated with ActiveX controls have also contributed to their decline in usage.