What are Windows .INF files for and how do they work?

Files with extension .INF They play a key and often little-understood role within the Windows operating system. Although they may go unnoticed by most users, their presence is essential during processes as important as installing drivers. hardware, device configuration or even the automatic execution of certain removable media. Since many questions and problems arise around these files and their handling, it's important to fully understand what they are, how they work, and what precautions to take when interacting with them.

In this article we are going to explain in great detail What are Windows .INF files used for?, how they're structured, what processes they're involved in, what risks they pose, and best practices for managing them securely. We also cover advanced technical aspects, tips for resolving common issues, and answer the most frequently asked questions about this type of file.

What is an INF file really?

An INF (Information File) file is a plain text file. It stores instructions and parameters for installing software, drivers, or automatically configuring devices in Windows. This format isn't exclusive to a single platform, although it's primarily used on Microsoft systems. Basically, the INF file acts as a 'script' that tells the operating system how to copy files, modify the registry, install services, or make other changes during an installation or configuration process.

The contents of INF files are divided into structured, formatted sections, each designed to perform a specific task. For example, one section might specify which files to copy, another what changes to make to the Windows registry, another might allow an installer to automatically run when a device is inserted, and so on.

Main uses of INF files in Windows

The usefulness of INF files in Windows is much broader than meets the eye. The main scenarios in which they are used are detailed below:

• Installing hardware drivers: When you connect a new peripheral (printer, mouse, graphics card, etc.), Windows consults INF files to know what files to copy, how to configure the device, and what parameters to register with the system.
• Automatic device configuration: INF files allow you to define specific options for each device and can intervene in the process of making hardware work correctly without manual intervention.
• Autorun media (autorun.inf): The well-known 'autorun.inf' is a special case found on CDs, DVDs or memory sticks USB and is used to tell Windows what to do (for example, start an installer) when that media is inserted into the computer.
• Installation of specific software or additional components: Some programs use INF files during the installation process to integrate files and modify settings beyond what the standard installer allows.

Therefore, INF files not only make the user's life easier, but They are essential for the operating system to be able to adapt its operation and resources to the needs of each new peripheral or component installed..

Structure and technical content of an INF file

A vital aspect of understanding INF files is their internal structure. These files are organized into sections clearly delimited by bracketed headers, and each section is designed to fulfill a specific function in the installation or configuration process.

In addition to these standard sections, INF files may include private sections whose format depends on the application using them. These sections allow you to store custom information that only a specific application will be able to use or interpret correctly. The Windows Setup API provides functions such as SetupGetLineText or SetupGetIntField to extract specific information from these areas.

INX files and automatic INF generation

There is a related format known as INX, which acts as a "template" version of the INF. INF files include string variables that represent variable information, such as the system version, architecture, or manufacturer name. Tools like Build or StampInf do the work of replacing these variables with actual values when creating the final INF file. This automation is very useful for hardware manufacturers or developers who need to distribute devices that support multiple environments or versions of Windows.

How driver installation works via INF

When you connect a new device, Windows looks for related INF files to determine how to proceed with the installation. The system analyzes the sections of the INF to determine which drivers to apply, which files to copy, which values to add to the registry, and whether to install additional services or modify existing files. For this reason, most software packages drivers include their INF file and often the user himself can force its use in the Device administrator selecting the option to install the driver manually from a local folder.

On modern versions of Windows, such as Windows 8, 10, and higher, security has been strengthened It is mandatory that INF files be digitally signed along with their associated catalog (.cat) file. This ensures the integrity and authenticity of the driver package, preventing the installation of malicious or altered software.

Secure signing and installation process for INF files

Windows requires INF files and their corresponding security catalogs (.cat) to be digitally signed on most modern systems. The general process for signing an INF for installation in Windows 8 or later involves several steps:

1. Generate the .cat file from the INF with specialized tools such as Inf2Cat included in the Windows Driver Kit (WDK).
2. Get or create a digital certificate which will be used to sign the .cat file. This certificate can be obtained from a certification authority (CA), or a test certificate can be created for non-commercial environments.
3. Sign the .cat file using SignTool, another tool provided by Microsoft in the WDK. Depending on the certificate type, signing is done by specifying either the certificate name or the associated .pfx file.
4. Install the public certificate on the target system before proceeding with the installation. This way, Windows trusts the digital signature and allows the INF to run.

It's important to know that Windows 7 does not require this requirement, so installing unsigned INFs is possible, although less secure. For development or testing purposes, test certificates can be used, but for final distribution, it's essential to use valid certificates recognized by Microsoft.

Other uses and related scenarios

In addition to those mentioned above, INF files appear in various situations:

• Autorun.inf: This is the file used to automatically run installers or other actions when physical media such as CDs, DVDs, or USB drives are inserted. Improper handling can facilitate the spread of malware, so Microsoft has restricted its use in recent versions of Windows.
• Configuring older modems and devices: It used to be common to find specific INFs for advanced configuration of modems, network cards, etc., allowing granular adaptation of the hardware to the user's needs.
• Packaging of components downloaded from the Internet: Sometimes, downloading components from remote servers includes an INF file to facilitate their automatic integration into the system, avoiding complex manual interventions.

Common problems when opening and using INF files

Not everything is positive when it comes to INF. Various problems can arise, both for technical reasons and due to security flaws or incompatibilities. Some of the most common are:

• Incorrect file associationIf the system doesn't know which program to use to open an INF, it will display error messages. Normally, using Notepad or plain text tools is sufficient, but, except for advanced editing, there is no need to open them manually.
• Version incompatibilitySome applications require INF files generated for a specific version of the software or operating system. Using the wrong version may result in installation errors or hardware malfunctions.
• INF file corruption: If the file is corrupt, has been modified inappropriately, or has become infected with malware, the installation may fail or the system may display warnings.
• Inconsistent registry settings: Accidental deletions or incorrect registry changes to INF files may prevent associated devices from functioning properly.
• Problems with the associated software: If the application required to use the INF is not installed or is corrupted, the installation process will not run correctly.

To resolve these incidents, it's a good idea to check the file's integrity, verify that you have the correct version of the application, and make sure it hasn't been affected by viruses or malware.

Security risks and recommendations

One of the most notable dangers of INF files is their potential to be used as an infection vector. In particular, Autorun.inf files have historically been used to spread malware which runs automatically when removable devices are inserted. As a general rule:

• Do not manually open INF files from unknown sources, especially if they have arrived by email or have been downloaded from unreliable pages.
• Always run an updated antivirus before handling or executing them.
• Do not modify INF files unless you know what you are doing.; an incorrect instruction can destabilize the system or render a device unusable.

To open or edit INF files, you can use tools such as Windows Notepad, TextMate, or any plain text editor, always taking extreme precautions.

Programs capable of manipulating INF files

If you need to view or modify the contents of these files, the following programs are suitable:

• Windows Notepad: Ideal for simple editing or quick reference.
• Microsoft Windows: The operating system itself recognizes INF files during the installation of drivers or devices.
• TextMate: For advanced users in environments Mac who need to inspect the contents of an INF exported from Windows.

Related article:

INF Files in Windows: What They Are and What They're Used For

Isaac

Passionate writer about the world of bytes and technology in general. I love sharing my knowledge through writing, and that's what I'll do on this blog, show you all the most interesting things about gadgets, software, hardware, tech trends, and more. My goal is to help you navigate the digital world in a simple and entertaining way.