1) You will need a small container, about 150-200 red or white matches, a floppy you are willing to destroy, a simple nail file,clear nail polish, and a computer to destroy.
2) Take all the matches and grind the powder from the heads of them off with a file. (There are Dollar Stores that sell 500 matches for a $1)
3) Collect all the powder into your container and set it aside.
4) Take apart the floppy carefully, by opening one corner of it and slowly pry apart the rest. Be very careful you do not break anything.
5) Put an even but thin coat of clear nail polish on the black center part of the floppy disk.
6) Next take the filed match powder and evenly sprinkle it over the black part of the floppy.
7) Inside of the floppy you will notice two circular pieces of almost paper like material. Pull them out and dispose of them.
Now put the floppy back together, as best as you can so it doesn't look obvious it was tampered with.
9) Have fun with it, but be responsible.