Imagine that you've opened a document sent to you by a colleague. She's told you that it's got information in it that you need to review, and that it performs a set of actions that may help you with your work. (The set of actions is called a macro; more about that in a moment.) But right now you can't get the document to work as described by your colleague. What's going on? Is it broken?
No, it's not broken. Although macros can be very useful, they can sometimes contain malicious code. Any potential security risks that can be identified are automatically disabled in Word 2007, Excel 2007, PowerPoint 2007, Access 2007, Publisher 2007, InfoPath 2007, Visio 2007, and Outlook 2007 files.
As shown in the picture, you'll know when something has been disabled because a helpful message appears in the Message Bar to tell you. You'll know it's related to a security issue by the shield icon that appears on the left, and you can read the text in the bar to find out more.
The best way to stay safer is to do nothing. Yes, as with suspicious e-mail attachments, the best thing to do is not to touch macros. It's surprising how often you just want to look at a file and have no need to ever enable anything.
Warning If you change any of the default security settings, potential security risks might not be automatically disabled. But as long as you don't change the behind-the-scenes security settings, the Message Bar will always appear when Office has disabled something in a file that is potentially destructive.