You can also password-protect add-in workbooks so that a password is required before your add-in can be opened. This is accomplished through the File/Save As menu item in Microsoft Excel. Note, however, that password-protected add-in workbooks cannot be loaded using the Add-In Manager. These workbooks can only be loaded manually, which potentially allows the user to turn off all your macros using the virus-protection dialog. Most add-ins are useless without their macros!