How to make an Undeletable File

This sets the a file to become a system file also hidden and archive property.

Use command prompt (start --> run --> cmd)

Code:

attrib +s +h +a filepath\filename

The command explained

attrib : States we are changing the "Attribute" of something
+s : This variable makes the "Attribute" of a file into a system file
+h : This variable makes the "Attribute" of a file hidden
+a : This variable makes the "Attribute" of a file archived

Simply customize it if you do not want to make it hidden or you don't want to etc..