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· 6 min read

Excel-DNA version 1.6 is now available for testing as pre-release version 1.6.0-preview3 from the NuGet package repository. The extension libraries ExcelDna.Registration and ExcelDna.IntelliSense also have matching releases. ExcelDnaDoc should follow in the coming weeks.

The main focus for version 1.6 is to provide a first preview of the support for add-ins that target .NET 6. As a prerequisite to adding the .NET 6 target, we’ve also added support for new SDK-style project files and NuGet references (also great for projects that target .NET Framework). I’ve also taken the opportunity to tweak the Excel-DNA packing mechanism a bit in an attempt to avoid some of the false positive anti-virus detections we’ve seen recently. I’ll briefly discuss these (in reverse order) below, but first a word about our sponsors.

GitHub sponsors

Excel-DNA is now registered on GitHub sponsors – see Thank you very much to everyone who has already signed up – your contributions are directly funding further development.

If you use Excel-DNA and would like to encourage future support and ongoing development, please sign up as a GitHub sponsor for the project. GitHub sponsors will also have access to a private repository of sample projects where I hope to add additional tools and documentation over time.

I had previously considered the .NET Core / .NET 6 support as a good point to switch to a commercial model for Excel-DNA. However, the benefits of being an open-source project with a permissive license have been significant. So, if possible, I hope to continue with the core library as free and open source software, where further development is funded by the sponsors.

For those in a corporate setting using Excel-DNA extensively or in a mission critical role, I also offer an annual corporate support agreement. Please contact me directly if you are interested in more details.

Anti-virus false positives

Over the last year we’ve seen a number of anti-virus and security programs identify Excel-DNA add-ins as security risks, including false positive detections that delete add-in files by the default Windows Defender service. It seems that these detections were triggered by some malicious Excel add-ins that have been built using Excel-DNA, with the anti-virus heuristics subsequently identifying all Excel-DNA add-ins as problematic. For some security vendors, including Microsoft, we’ve been able to report this false positive detection and they have updated their signatures accordingly. But in many cases the Excel-DNA version 1.5 add-ins are still being flagged.

It seems the main heuristic used to detect Excel .xll add-ins as problematic is the presence of executable assemblies as resources in the .xll library. Excel-DNA uses the packing of assemblies as resources in the .xll to simplify the add-in distribution, in many cases making possible a single file (or two files for 32-bit and 64-bit) add-in distribution.

For this version there are two changes which may help with these false positives.

The first is that packed files are now encoded, so that they are not detected as embedded executable code directly. In my testing that change removed the false positive detections at least in the Microsoft products. However, at least one other user has reported still seeing problems with this version, so it does not seem like bulletproof solution.

Another option has been contributed by user @Phundamentals (thank you!), to add a project property which disables the compression of packed files.


Should these mitigations not be enough to reduce most false positives, we could also introduce an option where there are no packed files at all (currently the managed Excel-DNA assemblies are always packed).

There have also been some indications that signing the final add-in library helps reduce false positive detections.

In all cases I do encourage developers to report the false positives to their anti-virus or security vendor. Their software is mistakenly identifying and blocking legitimate add-ins from running.

Developers of malicious add-ins are welcome to contact me for sponsored licenses of an alternative add-in framework.

PackageReference and SDK-style project files

The main ExcelDna.AddIn NuGet package now supports references in SDK-style project files. For new projects, this means that a .dna file is no longer added to the project automatically, and if not present will be created and output at build time from project properties. Existing projects with customized .dna file(s) will work as they did before.

For a new project, a simple project file might look like this:

<Project Sdk="Microsoft.NET.Sdk">


<!-- We don't need the extra 'ref' directory and reference assemblies for the Excel add-in -->

<!-- We need all dependencies to be copied to the output directory, as-if we are an 'application' and not a 'library'.
This property also sets the CopyLockFileAssemblies property to true. -->

<PackageReference Include="ExcelDna.AddIn" Version="1.6.0-preview3" />


Various additional properties can be set in the project file – see the example here

.NET 6 support

Excel-DNA version 1.6 (finally!) includes support for add-ins that target .NET 6. Most Excel-DNA features seem to work, including the COM-based features like RTD-based functions, ribbon and CTP extensions. However, there has been very limited testing and you should consider the .NET 6 support as an early preview.

Update the TargetFramework tag in an SDK-style project file to the .NET 6 (Windows) target:


or build for both .NET Framework and .NET 6, which allows you to test both targets:


End users of the add-in will need to have the .NET 6 runtime installed. (To include the runtime files as part of the add-in will not be supported, but an installer program might check and install the runtime.)

A hard limitation of the .NET core series of runtimes (.NET 5 / 6 / 7 etc.) is that only one version of a .NET core runtime can be loaded into a specific process. The core runtime can still be loaded concurrently with a .NET Framework runtime (e.g. .NET Framework 4.8), although this is not a configuration officially supported by Microsoft. Excel-DNA will try to support add-ins targeting a .NET Framework running together with .NET 6 add-ins, but there is not planned to be any support for the future .NET 7 runtime. Fortunately .NET 6 is a ‘Long-term Support’ (LTS) release and will be formally supported until the end of 2024, so we can keep targeting .NET 6 for a few years. There is also some work on the horizon that make ahead-of-time compilation of .NET libraries (like the Excel-DNA add-ins) viable, bypassing the concurrent runtime issues. So I do expect a future path beyond .NET 6, though that is not an immediate concern.

I look forward to bug reports, questions and other feedback about the .NET 6 support (including whether it works at all). Support for modern .NET has been a long time coming and ensures that Excel-DNA can take part in the exciting future evolution of .NET.

After 16 years I am still amazed by and deeply appreciate the support and enthusiasm for Excel-DNA. Last but not least I want to thank Sergey Vlasov for his calm and consistent efforts that are now driving the project forward.


· 5 min read

Excel-DNA version 1.5

A release candidate for the next version of Excel-DNA is now available for testing. Please try out this update, and let me know if you run into any problems or whether you are able to confirm that your add-in still works correctly. I expect to make a final release in a few weeks.

This update includes a completely new implementation of the core marshaling, replacing code that I initially wrote in 2005. I’ve also done some internal refactoring to prepare for supporting the .NET 5+ generation of runtimes. Finally, a few improvements were made to improve add-in load times when many functions are registered. Improved resilience in hostile anti-virus environments were also implemented since the last release.

Modernising the marshaling code has resulted in two notable changes of the minimum requirements for using Excel-DNA.

  • Only .NET Framework versions 4.5.2 to 4.8 are supported, and
  • Excel 2007 or newer is required, dropping support for the oldest versions of Excel.

UPDATE NOTE: If you are updating the NuGet package on a project that currently targets an older version of .NET (e.g. .NET Framework 4.0), you should change the target framework for the project to .NET Framework 4.5.2 or later, before updating the NuGet package. Otherwise you may get one of the following problems:

  • The package install script may not run when the new package is installed. This leaves the project with a file called “_UNINSTALLED_xxxxx-AddIn.dna”. In this case, uninstall the ExcelDna.AddIn package, update the project target framework, and then reinstall. You might need to restart Visual Studio to complete the package updates.
  • Error messages stating “Error CS0246 – The type or namespace name ‘ExcelDna’ could not be found (are you missing a using directive or an assembly reference?)”. This also indicates that the target framework is not supported and should be updated, after which the errors should be resolved.

Apart from the new minimum requirements, the new release is a highly compatible update and you should not expect any issues or significant behaviour changes after updating.

Thank you to @ittegrat and @augustoproiete for their contributions to this version.

The following prerelease packages are available on NuGet:

  • ExcelDna.AddIn.1.5.0-rc1
  • ExcelDna.Integration.1.5.0-rc1
  • ExcelDna.IntelliSense.1.5.0-rc1
  • ExcelDna.Registration.1.5.0-rc1
  • ExcelDna.Registration.VisualBasic.1.5.0-rc1
  • ExcelDna.Registration.FSharp.1.5.0-rc1

GitHub Sponsors

Excel-DNA is now registered on the GitHub sponsors program. This lets you sponsor future Excel-DNA development, and also gives access to direct support for your Excel-DNA projects. Billing for the monthly sponsorship is through your GitHub account, making it easy to add sponsorship of open-source projects to a corporate GitHub account.

If you are using Excel-DNA and would like to see further development and ongoing support, please sign up as a sponsor. A big thank you to those users who were the first to do so: @PierreYvesR, @terryaney, @mhouldsworth @KoosBusters and one private sponsor.

I’ve set up three levels of monthly sponsorship subscriptions:

  • Individual – $14 pm. For power users and developers making add-ins for personal or limited use.
  • Team – $170 pm. For smaller development teams in a company, those publishing add-ins externally or using more advanced add-in features.
  • Corporate – $850 pm. For larger companies with mission critical applications or multiple development teams.

For the Team and Corporate sponsorship levels I am also available for some monthly direct support sessions to help deal with problems or advise on your add-in projects.

The direct corporate support contracts are available as before, with bespoke agreements and extensive direct support. Thank you very much to the existing corporate partners who have supported Excel-DNA over the past decade and continue to ensure the project’s viability.


The development work for Excel-DNA will next address two areas:

  • Improved support for SDK-style project files and a PackageReference import of the main NuGet package. The newer .NET project templates and build tools are based on the SDK-style project files, so updating to support these even when targeting .NET Framework will be a big step forward. The main hurdle so far has been the install script and build tasks which depend on the older packages.config style NuGet implementation.
  • Support for the .NET 5+ generation of runtimes. I’ve made some progress towards the new add-in hosting code required for loading the .NET 5+ runtime, but getting to an implementation that can be supported for the future and work together with existing add-ins still needs a lot of work. The .NET 5+ runtime versions have more limited isolation capabilities, and different versions cannot be loaded side-by-side in the process. This might require us to standardise on a specific version like the .NET 6 Long Term Support release as the single supported .NET 5+ runtime target.

Thank you for your ongoing enthusiasm for Excel-DNA and the super-power combination of .NET and Excel. I look forward to your thoughts and feedback.