My question is...what is d2.exe?

When I woke up today, my brother had done a system restore on our computer, and its been slow ever since. I went to check the task manager and something caught my eye...there were a bunch of "d2.exe"s and they seemed to be the only processes taking up CPU. Also, there are quite a few of them (about 14 of them). So I wanted to know, is it safe to end all of those processes? Quick responses would be VERY much appreciated!