So I have only recently started playing Dark Souls, and I was hovering around soul level 25 the other night after reaching the Undead Parish, and decided to reverse hollowing for the first time. Predictably, I got invaded rather quickly. At first, my invader was just hanging out, taunting me. I had my shield up and got in a few hits - somehow, I earned almost 80k souls just hitting this guy. He eventually killed me, and left. I was able to run back and collect all 80k+ souls.
Later, the same guy invaded again and went on the attack. With my shield up, every time I blocked an attack, I got a ton of souls. I ended up with 1.6 million when he killed me. Again, I was able to go back and collect them, boosting my soul level to 96.