I was spearfishing with a buddy (dive flag flying on boat) with no one on baord the boat while we were down (yes, I konw this is not the bset thing to do) and surfaced as some other guys were getting ready to board my boat. We were 30 miles offshore with no other vessels within sight. i quickly climbed up my ladder, and we both left the bands on our spearguns engaged. They said they"were just trying to make sure everything was OK since they didn't see anyone on the boat", but I think they were either going to steal from my boat or steal my boat. I discretely had my hand on the AR-15 in my storage locker while I thanked them for their concern. They left the area after this. Since they did not actually board my boat, there was no point in calling the authorities. i no longer dive without someone tending the boat. I wonder if the situation would have been different if I was not flying the diver down flag. Did it act as an invitation to try and board my boat while we were diving? I feel lucky that the situation turned out OK.