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Excel tip: What is an Add In?

Date: 5 september 2001

What is an Add In?

An Add In is a workbook with custom commands and functions that can be used with Excel. Add In's are used to distribute macros, userdefined functions or custom solutions to other users.
When you save a workbook as an Add In, the content is "compiled" and protected so that the source code is (usually) not visible and editable by other people. You can find tools on the Internet that can "crack" this protection from Add In's made for Excel 5/95 and Excel97, but ordinary users will usually not be able to see or edit the contents of an Add In.
Add In's can be installed by opening the file as you open an ordinary workbook. You can also install the Add In by saving it to the Library folder and installing it from the Add In Manager with the menuchoice Tools | Add Ins.... When you install an Add In the custom functions are available to the user, and any userdefined menus in the Add In will also be added to the existing menus in Excel.
Add In's installed by the Add In Manager can be uninstalled by removing the checkmark in the list of installed Add In's in the Add In Manager.
Add In's can also be installed and uninstalled by using VBA-code

How secure is the Add In source code?

The source code in an Add In is poorly protected against users that are determined to take a look at it. There are both (almost) free tools and commercial tools available that can "decompile" the Add Ins (for all Office-applications). If you need one you only have to search the Internet. Maybe the source code protection is more reliable in the COM Add-Ins used by Office 2000?

How to create an Add In in Excel97

Add Ins in Excel97 are saved differently from the previous versions of Excel:
  1. Start the Visual Basic Editor by pressing Alt+F11.
  2. Select Debug | Compile VBA projectname. In previous versions of Excel the VBA-code was automatically compiled when you saved the Add In. This is no longer true, you have to do it yourself before you save the Add In.
  3. If you want to lock the project from viewing you can select Tools | Properties for VBA projectname. In this dialog you activate Protection and check the option Lock project for viewing. Fill in a password and click the OK-button.
  4. Activate Excel by pressing Alt+F11.
  5. Select File | Save asâ€.
  6. Change the option Filetype: to Microsoft Excel Add In (*.xla) (the last choice in the dropdown).
  7. Click the Save-button to save the workbook as an Add In.
The locking of the project will not take effect until you close and re-open the workbook.

You can convert a workbook to an Add In by changing the property IsAdd In to True for the ThisWorkbook-object. This must be done from the Visual Basic Editor. When the property is changed you can save the workbook by clicking on the Save-toolbarbutton.

Setting a Password for Your Project

To ensure that a user doesn’t inadvertently or purposely change any of the code in an add-in that you’ve created, it’s a good idea to protect the add-in by assigning a password to the Visual Basic for Applications project associated with it.
  1. In Microsoft Excel, open the project you want to protect.
  2. Open the Visual Basic Editor.
  3. In the Project Explorer, select your add-in project. (If the Project Explorer isn’t displayed, click the Project Explorer button on the Visual Basic Editor toolbar.)
  4. On the Tools menu, click <YOURPROJECT>Properties</YOURPROJECT>.
  5. On the Protection tab in the <YOURPROJECT>Properties</YOURPROJECT> dialog box, select the Lock project for viewing check box.
  6. In the two text boxes under Password to view project properties, type the password you’ve chosen, and then click OK.

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