Programming Excel with VBA and .NET

Security Layers

When it’s cold you dress in layers , and security works the same way. The outer layer is a firewall, preventing attacks from the Internet. Next, virus detection software scans permitted attachments and other files from bringing in malicious code. Then, operating system security defines users and their permissions. Finally, Excel provides its own security layer.

Data most at risk is that which is shared outside of these layers, such as a workbook posted on a public server. In that case, Excel becomes the primary security layer. Of course not all data needs the same level (or type) of protection. Therefore, Excel itself provides layers through these security approaches:

• Password protection and encryption control read and write access to workbooks.

• Worksheet protection password-protects items within a workbook and alternately can authorize changes based on user lists.

• User-based permissions allow authors to limit the rights of others to read, change, print, copy, or distribute a document. Permissions can also set an expiration date for a document.

• Digital signatures identify the author of a document, ensuring that a document is the authentic original—not a modified or spoof copy. Signatures can also be applied to macros and ActiveX controls to ensure their code is from a trusted source.

• Macro security levels determine what level of trust is required before Excel will run code included in worksheets, templates, add-ins, or Smart documents.

• ActiveX control security levels similarly ...