Excel doubt

I have written a function which writes data to a password protected excel worksheet, so that the user cannot manipulate with the worksheet unless he/she knows the password. But the problem is the user can copy the cells of the worksheet and paste it to another worksheet and can make the necessary manipulation(s). Is there any way where by I can make the copy menu of Excel-worksheet enabled=false at run-time.

Examples would be highly appreciated.

Well,
I suggest just encryption and decryption,
There are various methods available of encryption

Gary