At soul level 91, I just did a forest covenant invasion.  Killing the guy landed me 887k souls.  WHAT THE FUCK.

He probably was duping souls. 
 
I know that I gave someone 500k souls once for dying. (non dupe). I haven't gotten many from people though. 

At soul level 91, I just did a forest covenant invasion.  Killing the guy landed me 887k souls.  WHAT THE FUCK.

I killed a rather jaunty fellow and received 700k souls. Enough to level me 5 times.

Pip pip.

At about level 45 I shanked three dudes one night that each netted me between 100-150k each

about 1,500,000 souls, most definitely a guy using the dragon head trick.

Hmm, think I should try this invasion thingy for myself :)

only some 20 k :( .... granted here in mexico there arent many players so theres not much pvp

Just got 500k souls for invading a guy. Pretty nice, got me from 70-84 and I poured all of those points into vitality.  
 
e: just got 870k souls lol.  
 
e2: and now 270k. I've gotten over a million souls tonight from PvP. 
 
e3: another 870k. Jesus christ people have a ton of souls around SL100. If someone kills me atm they would get 1.2 Million souls lol. 

Fought a bunch of people in Anor Londo for the Darkmoon Covenant, and 2 of the guys (maybe the same guy) dropped a bit over a million souls each time.

Fought a bunch of people in Anor Londo for the Darkmoon Covenant, and 2 of the guys (maybe the same guy) dropped a bit over a million souls each time.

@Nadril: I don't think so, but maybe, I was running around with a lightning Iato/Uchi and Gold-Hemmed Torso and head, with Havel's Gauntlet's and Legs.

I was on NG+ with SL 135 when i invaded one and killed him he gave me 215million souls, i boosted my character 300 level!

Huge possibility that your opponent was hacking his game to have infinite amount of souls. It happened to me and Dark Souls 2 when playing with a friend. He invaded. We killed him and I an obscene amount of souls that fucked up my Souls Memory level.

@mordukai: Hopefully im not considered a hacker if i kicked his ass and got his souls right? i considered him as a hacker but was not sure bout it

I don't think you have anything to worry about. If it's Dark Souls 2 then I really don't know. I'll admit, I used a trainer after that to get my SM down to where it was so I can coop with my friend and I got soft banned for it. I am not griping over it. I knew the risk I took. I will say that SM is a huge mistake on FROM's part. I don't think there's many Dark Souls 2 players that agree that it's a good system.