What is the ISU file format?
An .isu file is a proprietary binary log created by InstallShield (now published by Revenera, formerly Flexera Software) during software installation. It records everything the installer placed on the system - installed files, registry keys, shortcuts, and registered COM components - so the uninstaller can reverse the installation cleanly.
The .isu file is written to the application's installation directory (for example C:\Program Files\<AppName>\) or a dedicated uninstall folder during setup. Without it, the InstallShield uninstaller (iun*.exe) cannot perform a clean removal and the application may require manual cleanup or a third-party tool.
End users should never open or modify .isu files directly. The format is proprietary and undocumented; it is read exclusively by the InstallShield runtime. The binary structure varies across InstallShield versions with no public versioning scheme.
The modern standard for Windows software installation is the .msi (Windows Installer) format, which replaced InstallShield's proprietary log mechanism for most commercial software released after the mid-2000s. Legacy ISU-based installers remain common in enterprise and industrial software shipped before that transition.
- Companion
.issfiles store silent-install response scripts for unattended setups. - The format is Windows-only with no Mac or Linux equivalent.
- Revenera's current InstallShield supports both legacy ISU projects and modern MSI-based packaging.
Security & safety
RISK: LOWISU files are passive data files read only by the InstallShield runtime; they contain no executable code and cannot run on their own. Risk arises only if a malicious installer plants a fake ISU to confuse the uninstaller, which is rare.
Format details
in a nutshellPrograms that open ISU files
Windows1 app
InstallShield (Revenera)
Paid Used internally by the InstallShield uninstaller; load via setup.exe /x or the Control Panel uninstaller. Technical details
deep spec| Format type | Proprietary binary installer log/script |
| Encoding | Binary |
| Byte order | Little-endian |
| Magic bytes | None publicly documented; header bytes vary by InstallShield version |
| Typical file size | 1 KB - 500 KB |
| Associated OS | Windows only |
| Storage location | Application installation directory or dedicated uninstall folder |
| Runtime consumer | InstallShield uninstaller (iun*.exe); not user-accessible |
| Internal versioning | Varies by InstallShield version; not publicly specified |
| MIME type | application/octet-stream |
| Modern successor | .msi (Windows Installer) - now the standard for commercial Windows software |
| Related formats | .iss (silent script), .ins, .msi |
| Released | mid-1990s (InstallShield for Windows era) |
| Latest version | InstallShield 2023 / 2024 (Revenera) |
| Specification | docs.revenera.com |
ISU conversions
Community Q&A
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