Microsoft Office security

In the interests of data security, Microsoft Office 2000 and later versions have their security settings set to high by default. To view or change your security level in Excel or Word, choose Tools | Macro, click Security, and click the Security Level tab.

• If you have your security level set to High (the default setting), then communication with external DDE Servers will not be available unless they are digitally signed and trusted. What you see in Excel cells that use the DDE function is #N/A , and with no additional explanation as to why the DDE functions aren't working. The High security setting (if selected) does not appear to affect the use of remote DDE Client requests with those Office applications as DDE Servers.
• If you set your security level to Medium, you are asked if you want to run any DDE Servers that are not digitally signed and trusted and that are referenced by DDE functions.
• If you set your security level to Low, external DDE Servers are run regardless of whether they are digitally signed and trusted, or not.

• Note: If you need to manipulate another application's objects from Microsoft Office, consider using OLE Automation.