I have had many questions regarding this topic from a number of users. Now that I've found this article from Microsoft Office Online, I wanted to share.
"Microsoft Office Access 2007 uses a new security model that is simpler than earlier versions. In Access 2007, you indicate whether you trust a database, and all other security decisions are made for you automatically, based on your trust decision. This article contains an overview of how trust works in Access 2007, how it differs from security in earlier versions, and what factors you should consider when you decide whether to trust a database." Read the rest of the article.