On July 8, Microsoft reversed its February decision to block macros in Excel documents by default. Microsoft has said it will block Excel files containing macros if they are downloaded from the Internet. (Attackers use these decoys as a way to attack networks; in particular, ransomware and other types of malware can be launched from a plain old malicious spreadsheet.)

Microsoft still plans to introduce this lock, but only after “better experience”. In the meantime, there are steps you can take now so you don’t have to worry about changes in the future.

If you work for a firm that develops spreadsheets for their own internal office use, chances are the spreadsheet is not digitally signed. Signing machos is similar to how websites use SSL certificates to verify the legitimacy of a site. The hardest part of the self-signing process is deciding whether you want to purchase a code-signing certificate or use a self-signed certificate process. (I can tell you from personal experience that trying to purchase a code signing certificate is an expensive and cumbersome process. I don’t recommend this option except for large enterprises where the code signing process is routine.)

For everyone else, I recommend signing your Excel macros yourself. The tricky part is getting a program that allows you to do this. You will need to follow this Knowledge base article to locate the selfcert.exe file on your computer. In my case, the file is located in “C:Program FilesMicrosoft OfficerootOffice16” (if you are using a 64-bit version of Office). Run the selfcert.exe program and name the certificate something descriptive, such as MyExcelFiles.

In the search box on your Windows computer, type mmc.exe to launch the management console. Click on the file, then on “add/remove a snap-in”, then on “include certificates” and add it to the management view. You want to add it to “My Account”. Click on certificates > current user and then on personal certificate store. You should now see this “MyExcelFiles” certificate in the certificate store. You can double-click on it to view the certificate. (It should say that the CA root certificate is not trusted; this is normal for a self-signed certificate.)

Now open the Excel file that you want to sign with your self-signed certificate. (You’ll need to add the Developer tab to your Excel spreadsheet if it’s not already showing.) After clicking File > More > Options, select Customize Ribbon on the left. Then select the “Main Tabs” on the right, select the “Developer” checkbox and click the “OK” button.

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