[For Educational Purposes]
-A web browser
Ever just need to quickly download a song for free?
1) Navigate to Goog|e
2) In the search bar type: intitle:index.of [This allows us to search for indexes, which are usually unprotected.]
3) After a space, type: -inurl:(shtml|html|htm|php|jsp) [This allows us to weed out some (not all) "junk" results.]
4) After a space, type: (mp3) [This is the type of file we want. You may add .wav's by typing (mp3|wav) instead.]
5) After a space, type song name in quotation marks. For example: "Joshua Tree"
6) Hit enter. Look for results that make sense. For instance, a result that mentions "U2" if we searched "Joshua tree" is very promising.
7) Click the result's "Cached" button. This will highlight the song title you inputted.
8) Right-click and save.
FU tl;dr Version
Paste: intitle:index.of "last modified" -inurl:(shtml|html|htm|php|jsp) (mp3) "song name" into Goog|e. Look for songs in the results.
Some advertisers know about this method. You may run into a fake link taking you to commercial website. It's annoying but harmless.