In excel, you can setup a file so that you need a password to open it
(Go to File -Save As. Click on Tools -> General Options) but this can
be bypassed using tools readily available online.
the better solution would be to use a 3rd party encryption software
to encrypt the file for you. If this is your standard confidential
info and not nuclear launch codes, try using WinZip to compress /
encrypt the file. You can use 256 bit encryption and it's rather easy
to encrypt / decrypt your file.
