So Blizzard created an online store which allows you to legally download games from their site. You do not need to purchase
anything. You only need to enter your CD-Key into there site (A CD-Key only works once on their site), then your account can legally download the game.
Steps to Download Diablo II:
1) Go over to
http://www.blizzard.com/store/
2) Create an account and verify it, if you do not have one.
3) When your logged in, hit the Account link in the top-right.
4) There should be four tabs on the right side, click the one that says Games.
5) You should now be at,
https://www.blizzard.com/account/management/games.xml
6) Click Add New Game
7) Add your Diablo II CD-Key in the input box provided.
8) Repeat Step 6 and 7 for your Expansion CD-Key.
9) Now in your Games page, you should see Diablo II and Diablo II: Lord of Destruction.
10) Download the two downloaders (Choosing Mac or Windows).
11) Open up the classic D2 Installer, and choose a location for download.
12) Once completed, install it.
13) Repeat 11-12 for expansion.
Note: You are given a new rendered 26 character cd-key from the site that you must use for the installation. I assume you can use cd-key changer afterwards to change it.
Legally Download Diablo II! Jun 12 2015So Blizzard created an online store which allows you to legally download games from their site. You do not need to purchase anything. You only need to enter your CD-Key into there site (A CD-Key only works once on their site), then your account can legally download the game.