Privacy is an important watchword these days, and Excel can help you hide sensitive customer information such as Social Security Numbers or credit card numbers.
Simply use CONCATENATE to combine a generic text string representing the missing digits with the last four digits. That's enough information for, say, a customer service representative to confirm an identity without sharing the full number to employees who don't need access to it.
To do this, use the formula like so:
In the example, the text string "***-**-" is appended with the 4 rightmost characters in cell A2:
Once you're done, you can Hide Column A:
Now, to lock it, go to the File menu in Excel 2010 and choose Protect Workbook, Protect Current Sheet:
Set a password and the workbook should be protected against unhiding the column:
But the data is still there if you need it and have the password.
It is a combination of basic operations, can be broken but still very good.