As a workgroup administrator, you might initiate or oversee workgroup security practices for protecting Excel workbooks. This section describes the options available in Excel for protecting workbooks. These options are independent of any additional security measures at the operating system level.

Excel incorporates the symmetric encryption routine known as RC4. RC4 is stronger than the encryption routine used in previous versions of Excel, known as Microsoft Office 4.x. Workbooks from previous versions of Excel are not as secure as password­protected workbooks in Excel 97 (Windows) or Excel 98 (Macintosh) format.

Note that strong encryption such as RC4 is banned in France. If a user’s locale setting in Regional Settings on the Control Panel is set to French (Standard), that user is not able to open an Office document that is password protected. Nor can the user save an Office document with RC4 encryption. The user can, however, use XOR encryption by saving an Office document with password protection.

Excel supports three levels of workbook file protection. All three levels are controlled by the author of the workbook, who is the user with read­write access to a workbook. The three levels of workbook protection are:

· File open protection : Excel requires the user to enter a password to open a workbook.

· File modify protection : Excel prompts the user to enter a password to open the workbook read­write. If the user clicks Read Only at the prompt, Excel opens the workbook read­only.

· Read­only recommended protection : Excel prompts the user to open the workbook read­only. If the user clicks No at the prompt, Excel opens the workbook read­write, unless the workbook has other password protection.

· On the File menu, click Save As.

· On the Tools menu, click General Options

(Figure 3.13)

· Do one of the following

To have Excel prompt the user to open the workbook read­only, select the Read­only recommended check box.

To require a password to open the workbook, type a password in the Password to open box, and then click OK.

To require a password to save changes to the workbook, type a password in the Password to modify box, and then click OK.

· When prompted, type the password again, and then click OK.

· Click Save.

In addition to protecting an entire workbook, you can protect specific elements from unauthorized changes. The elements you can protect are:

· Structure of a workbook : Sheets in a protected workbook cannot be moved, deleted, hidden, unhidden, or renamed, and new sheets cannot be inserted.

· Windows in a workbook : Windows in a protected workbook cannot be moved, resized, hidden, unhidden, or closed. Windows in a protected workbook are sized and positioned the same way each time the workbook is opened.

· Cells on a sheet : Contents of protected cells cannot be edited.

· Graphic objects on a sheet : Protected graphic objects cannot be moved or edited.

· Formulas on a sheet :Protected formulas cannot be edited. You can also hide a formula so that it does not appear in the formula bar but the formula results appear in the cell. On the Format menu, click the Cells command, and then select the Hidden check box on the Protection tab. You must then protect the workbook file.

· To protect cell contents including formulas, graphic objects, or scenarios, point to Protection on the Tools menu, and then click Protect Sheet.

(Figure 3.13)

· To protect the workbook structure or windows, point to Protection on the Tools menu, and then click Protect Workbook. Select the check boxes for the elements you want to protect.

(Figure 3.14)

· To prevent others from removing protection from the sheet or workbook, type a password in the Password box and click OK, and then retype the password in the Confirm Password dialog box.