13.3 Distributing Macros Safely.

Distributing macros safely ensures that your code remains secure, functional, and easily accessible by others while minimizing risks, such as malware or unauthorized changes. When sharing your Excel workbooks or add-ins that contain macros, it's important to follow best practices to ensure the safety of your macros and protect both your intellectual property and the users’ data.

Why Is It Important to Distribute Macros Safely?

• Security: Macros can be vulnerable to misuse or modification. Malicious code can be added to your macros by unauthorized users.
• Trustworthiness: If your macro is shared with others, it's essential to build trust by ensuring it does not compromise the user's system or sensitive data.
• Compatibility: Macros may not work properly across different Excel versions or environments unless carefully prepared for distribution.

Best Practices for Safe Macro Distribution:

1. Sign Your Macros with a Digital Signature
   • Why? A digital signature ensures that your code hasn’t been tampered with and is from a trusted source. When a user opens a file with a signed macro, they can verify that the macro is genuine.
   • How? Use a code-signing certificate to digitally sign your VBA code. This can be done in Excel by going to the Developer tab, selecting Visual Basic, and then choosing Tools > Digital Signature.
   Steps to Sign Macros:
   • Obtain a code-signing certificate from a trusted Certificate Authority (CA) or create your own self-signed certificate.
   • In the VBA editor, go to Tools > Digital Signature.
   • Select your certificate and apply the signature.
   • Save the workbook. The next time it is opened, users will see a message confirming that the macro is signed.
2. Distribute as an Add-in (.xlam) or Macro-Enabled Workbook (.xlsm)
   • Why? Distributing macros as .xlam (Excel Add-in) or .xlsm (macro-enabled workbook) ensures that the macro is easily accessible while keeping the code separate from the user’s original workbooks.
   • How? Save your workbook as an add-in (.xlam) or a macro-enabled workbook (.xlsm), which makes it clear that the file contains macros and ensures the code is bundled with the workbook.
   Steps to Save as Add-in:
   • After writing your macro, save the workbook as an Excel Add-in (.xlam).
   • To install the add-in, users simply go to the Add-ins tab in Excel and load the add-in file.
3. Avoid Using Macros That Rely on External Files or Links
   • Why? Relying on external files or links can create security risks or compatibility issues, especially if those external resources are unavailable or tampered with.
   • How? Whenever possible, make sure that all resources used in your macro are self-contained within the workbook. If you need to reference external data or files, ensure the path is reliable and the user can access the necessary files.
4. Provide Clear Instructions for Users
   • Why? Not all users may be familiar with enabling macros or using add-ins. Providing clear, easy-to-follow instructions ensures that users understand how to safely use your macros.
   • How? Create a README file or documentation explaining how to install and use the macro, what it does, and any precautions the user should take (such as enabling macros).
5. Use Trusted Locations
   • Why? Excel’s security settings may block macros from untrusted sources. To avoid this, distribute your macros in trusted locations where macros are allowed to run without warnings.
   • How? Advise users to save your file in a trusted location. Excel allows you to configure trusted locations under File > Options > Trust Center > Trust Center Settings > Trusted Locations.
6. Warn About Potential Risks
   • Why? Users need to be aware of potential security risks, especially when downloading or opening files from the internet or unknown sources.
   • How? Always include a disclaimer or warning about macros when distributing files, encouraging users to only enable macros from trusted sources.
7. Use Password Protection for Sensitive Macros
   • Why? If your macro contains sensitive data or logic that should not be exposed or altered by the user, password-protect your code (as explained in 13.2).
   • How? Lock the VBA project with a password to prevent unauthorized access, editing, or theft of your code.
8. Test on Different Environments
   • Why? Macros can behave differently on different versions of Excel or operating systems. Ensuring compatibility will prevent issues for users.
   • How? Test your macro on different versions of Excel (e.g., Excel 2016, 2019, Excel 365) and different operating systems (Windows, macOS) to ensure it works smoothly across platforms.
9. Consider Using a Custom Installer for Large Projects
   • Why? For large, complex VBA projects with multiple dependencies, using a custom installer can ensure that all necessary files are correctly placed in trusted locations and that the macro is installed properly.
   • How? Use third-party software to create an installer that automatically installs your add-in and any dependencies, ensuring users don’t have to worry about manually installing or configuring anything.

Potential Risks and How to Mitigate Them:

1. Malware or Viruses in Macros
   • Mitigation: Always sign your code and provide instructions on enabling macros only from trusted sources. Educate users to be cautious when enabling macros in unknown files.
2. Incompatibility with User Systems
   • Mitigation: Test your macro on multiple systems and Excel versions. Provide troubleshooting steps or offer assistance for users who may encounter issues.
3. Users Modifying or Misusing Macros
   • Mitigation: Password-protect your code to prevent unauthorized modifications. Provide clear documentation to help users understand how to use the macros correctly.

Conclusion:

Distributing macros safely requires a combination of security measures, clear instructions, and best practices to ensure your code is both functional and protected. By signing your macros, using trusted locations, and offering guidance, you can help users safely access and utilize your powerful macros without compromising security or functionality.