As i said before, just call diablo tech support and ask for a new cd-key, however, because i think that you just either gave yours out or are using a downloaded version of diablo, you can't. I apologise if i am incorrect, but still, it is unlikely that your CD was stolen, besides, who is going to post thier cd-key, if all you want is the single-player then just search for one, else you are skrewed, at most you can maintain a connection for one hour before someone sends you a kill command, while using a public cd-key.
actualy, u can get ur cd key stole, with starsucker... a very simple prog that use the port scan method to scan for a cd key, orig made for sc, works for w2 and d2 as well. cant get a pub, was a priv ver made by ann.
They are, you have a 1:100 chance in getting online with a stolen CD-Key. If you want to have a working CD-Key, download the whole list and use Onlyers CD-Key changer bot to make a big list of MPQ's so you have a 1:10 chance of getting on, but you have a 1:20 chance of getting kicked off at the first hour so that sucks, Suprisingly, after digging in Kazaa, I found a few CD-Keys that aren't used as much. Moral of the story, get a File Sharing Program before using the internet, the Files are less searched than the internet so they have a greater chance of working. And what i ment was that it is more likely that you gave your CD-key away, by accedint mostlikely, than it being stolen. Never share CD-Keys with friends, they might share it or they might be hacked.