What is the ISS file format?
.iss files are Inno Setup Script source files that define Windows software installers. Inno Setup is a free, open-source installer builder for Windows created by Jordan Russell in 1997 and currently maintained by Martijn Laan at jrsoftware.org.
An .iss script uses an INI-like section structure where each section, enclosed in [SectionName] brackets, controls one aspect of the installer. Common sections include [Setup] for general installer settings, [Files] for files to be installed, [Icons] for shortcuts, [Registry] for registry entries, and [Code] for embedded Pascal scripting. The [Code] section provides a full preprocessor and runtime scripting environment, enabling complex conditional installation logic.
The script itself is plain text - UTF-8 or ANSI for legacy scripts, with full Unicode support added in Inno Setup 5.1. It is compiled by ISCC.exe (the command-line compiler) or the Inno Setup IDE into a single self-contained Windows .exe installer. No binary data is embedded in the .iss file itself; all referenced installer assets remain as external files until compilation.
Inno Setup 6.x, released from 2020 onward, is the current major version. Its main free competitor is NSIS, which uses .nsi script files. .iss files can be edited in any text editor; Visual Studio Code offers syntax-highlighting extensions for Inno Setup.
Security & safety
RISK: LOWAn ISS file itself is plain text and cannot execute. Risk arises when you compile and run the resulting EXE installer - always review what a third-party ISS installs before compiling. Legitimate ISS files from open-source repositories are routine; be cautious with ISS files from unknown sources that claim to install commercial software.
Format details
in a nutshell- ISS Internet Security Systems / IBM Log File - IBM ISS (now HCL) network security products use .iss for scan logs and configuration; unrelated to Inno Setup.
- Unattended Windows Setup Answer File - Silent installer answer files recorded by Setup.exe -r and replayed with -s; also .iss extension, separate from Inno Setup.
Programs that open ISS files
Windows4 apps
Inno Setup
Open-source Open the ISS in the Inno Setup IDE; press F9 (Compile) to build the EXE installer. 
Notepad
Open-source Open and edit ISS as plain text; install the Inno Setup language plugin for syntax highlighting. 
Inno Script Studio
Freemium Open ISS file; provides syntax highlighting, wizards, and a built-in compiler. 
Visual Studio Code
Open-source Open ISS file; install 'InnoSetup' VS Code extension for syntax highlighting and snippets. Technical details
deep spec| Encoding | Plain text - UTF-8 or ANSI (legacy); full Unicode support since Inno Setup 5.1 |
| Structure | INI-like sections enclosed in `[SectionName]` brackets; each section controls one installer aspect |
| Key sections | `[Setup]`, `[Files]`, `[Icons]`, `[Tasks]`, `[Registry]`, `[Code]` |
| Scripting support | `[Code]` section provides a full Pascal-based runtime scripting language with preprocessor directives |
| Compiler | `ISCC.exe` (command-line) or Inno Setup IDE; outputs a single self-contained `.exe` installer |
| Preprocessor | `#define`, `#include`, and conditional directives supported for script-time logic |
| Unicode output | Full Unicode installer generation since Inno Setup 5.1 |
| Current version | Inno Setup 6.x (2020+) |
| License | Free and open-source (Inno Setup compiler); `.iss` scripts are user-authored |
| Typical size | 1 KB - 200 KB (source script only; referenced files remain external) |
| Platform | Windows only - both the compiler and the generated installer target Windows |
| Closest competitors | NSIS (`.nsi` scripts) and WiX Toolset |
| Released | 1997 (Inno Setup 1.0) |
| Latest version | Inno Setup 6.x (2020+) |
| Specification | jrsoftware.org |
ISS conversions
Community Q&A
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