Programming Excel with VBA and .NET

Macros and Security

When you open a workbook that contains code, Excel displays a security warning suggesting you might want to disable the code, as shown in Figure 1-29.

Microsoft included this warning because, once a user enables the macros in a workbook, that code has full access to the user’s system and can do some pretty nasty things (such as changing or deleting files) without the user knowing it. Microsoft deals with this problem differently in different programming tools, and in Excel Visual Basic they put the burden on the user for determining whether code should or should not be trusted.

Figure 1-29. Excel’s macro security warning is pretty dire

Unfortunately, users are often the least-qualified people to make this judgment. Who knows where ch01.xls came from or what it will do if I open it? The way to answer those questions is to add a digital signature. A digital signature identifies the author of the content or the macros contained in a workbook, template, or add-in. By digitally signing a workbook’s code, you add a unique identifier that says the code came from you (or your organization) and thus the user may have more confidence that the workbook won’t insert the word Wazoo in all your correspondence.

Tip

I once received a work-for-hire contract from Microsoft legal that occasionally declared Wazoo! I thought they were just checking to make sure I read the thing.... ...