By default, PowerPoint 2007 will be configured to disable all macros. The justification for this is that macros from unknown sources may contain viruses or other material that could potentially harm your computer. However, this is no reason to shy away from using macros from trusted sources. Just remember to take precaution and only open PowerPoint presentations from known parties or use an antivirus program to scan the files before using them.
To enable macros, first click on the Macro Security button in the Developer tab.

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When the Trust Center window opens, make sure the Macro Settings category has been selected. Check the boxes next to the options Enable all macros and Trust access to the VBA project object model. Click OK when finished to exit this window.

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If you’re still worried about contracting a virus, and you plan on viewing several third-party presentations that contain macros, you can narrow down which macros will run by selecting Disable all macros except digitally signed macros instead of Enable all macros. (For more information about digital signatures, see this article.) This will offer some added security when dealing with third-party macros, but it’s still not a total safety net. This option should never be used as a complete replacement for scanning macro files for viruses, but as an additional tool to help you judge the validity of the file.
For more tips and tricks, be sure to browse through the other items in Bright Hub's collection of Microsoft PowerPoint tutorials and user guides. New and updated articles are added on a regular basis, so bookmark us and check back often.