Here are instructions on how to encrypt a Microsoft Excel Spreadsheet
(Requires MS Office version 2002, a.k.a. Office XP, and newer)
Using Microsoft Excel, open the spreadsheet that you want to Encrypt.
Click on the Tools menu, click the Options tab, and then click the Security tab.
Click the advanced button. From the Encryption Type menu, scroll down and chose
RC4, Microsoft Enhanced RSA and AES Cryptographic Provider (Prototype). Leave the Key Length set to 128 and the Encrypt document properties check box, checked.
Now type a password in the "Password to Open" field, click okay.
You will get another dialog box asking you to Re-Enter your password. Please re-enter your password and click ok.
Remember: It is difficult to recover a password protected or encrypted file if you lose the password.