One of the challenges faced when controlling access to Excel workbooks is allowing users to view specific parts of a workbook while restricting them from viewing or editing the entire workbook. If a user is a member of the default site Visitors group, then they have the rights to view and download workbooks from any document library on the site. Users with these rights could view the entire content of the workbook if it is not otherwise protected. The recommended approach in SharePoint Server is to give users restricted rights on the document libraries that are set up as trusted locations for Excel Calculation Services. Two SharePoint Server permissions control this behavior at the site level: Open Items, which allows users to open a file in its client application such as Office Excel 2007, and View Items, which allows a user only to view the content of a workbook through Excel Web View but not to open or download the file. To implement this configuration, create a new security permission level for the site by copying the Read permission level and removing the Open Items permission. Then assign this permission level to a group that will hold all the users who should not have the right to open workbooks on this site. For more details on configuring site permission levels and groups, see Chapter 7, "Implementing Security for SharePoint Products."
Information Rights Management using Rights Management Server is not supported for workbooks that are accessed through Excel Calculation Services.