If I want to play Diablo connected it requires me to "Run As Administrator". This irritates me a lot, because I perceive it as a security risk. I suspect there is a possible registry fix to get it to run as a normal user. If you know of one please let me know. Thanks!
Diablo tries to open an incoming port when connecting to battle.net, wich is important for hosting multiplayer games. (Source: portforward.com)
Normally, a program doesn't need to have admin rights to do this, but on Vista and newer it has to "ask nicely" via UAC beforehand or an error occurs.
The problem is that Diablo (and Diablo II) were released well before Vista, so the program doesn't know what to do with the error and instead fails to connect.
This behaviour is normal if you run older games on Vista or 7, and I haven't heard of any remote exploits for that game. Even if there is one, I suspect the probability to be hit by something like this to be extremely low.
If the game hasn't been installed by Windows, then it will ask this question every time an application needs elevated privileges like accessing hardware (which Diablo does, eventually, like Sound and 3D video)
This might also be the case where the game has been installed on an external drive, or on a partition not formatted as NTFS.
If you are sure of the installation source and you just moved the game from one OS installation to another without really installing it (with Diablo it is actually possible, by just moving the whole directory), then it should be all right.
A Trojan horse or a virus would install itself only once and never ask again for permission, anyway.