This could very well be a bug. I have over 400 computers on my network, and my friend and I played on the Warlords map. We played for 8 hours!!! I've already written about this somewhere! Everything worked fine for me, and a computer attacked me around turn 60 and didn't bother me again (and why would it, against 3,000 skeletons and a level 30 hero!!!). The computers lost quickly. This is most likely due to the network. If this happened only once, then it's a network bug; if not, then it's a bug related to turn 30, because after turn 30, everything was fine for me. By the way, do you know how to play as each other?