I do understand it, it just isn't feasible.
Say we have 99 people, each of whom has submitted 2 shares.
Now lets say person 100 is the "attacker". They join the pool and submit 2 shares. Thus earning them an equal percentage. Then they leave, as they've hit the point in which they now have their equal share, and are simply maintaining a percentage from there on out, as opposed to gaining from nothing.
The round continues on for a few hours. Those 200 shares then turn into 20000 shares over time. Of which, 19998 belong to the first 99 people, and the last 2 belonging to the attacker who jumped ship.
The attacker has reduced their payout from 2% of the total, to 0.02% of the total.
The only way they could effectively attack the pool is to determine the total number of shares that 100% CFD would be, for the pool, and submit 2x that number of shares by themselves, then jump ship to another pool... and even then, that isn't stealing money from others, it's simply guaranteeing that they maintain their original percentage of the payout over time.
It's not extra earnings, it's just earnings. You cannot make more money than your average daily payout. If anyone claims to have done this, they got lucky once or twice, and the few times that they are dramatically unlucky will balance that out, thus maintaining the average.
Not true. Let me explain.
Lets say I contribute to 5% of the pool (which generates 100 shares an hr), thus I generate 5 shares/hr. I will make 2.5 bitcoins when a round finishes. This is true as long as I keep mining.
However, lets say this round is really long, and past some point (say 10 hrs - 1000 shares) I jump ship. When I jump ship, I still will make 2.5 bitcoins from my mining time from this pool if it hits immediately. If the pool hits 1 hour after I jump ship (hits the 11th hr), I will make 50*(50/(1000+95))=2.28310502 bitcoins. If another pool (lets say per-share) pays me more than (2.5-2.2831)/5 bitcoins per work verification, I will be making more bitcoins than just the 2.5 I would have made if I stayed in your pool. Also, for each additional hour after the time I jump ship, the amount extra that I make by jumping ship increases.
So I think my way is better. Just keep a sliding window (n hr) of the number of shares submitted by a user. And when we hit, split payout based on faction of work done in the past n hrs. Don't clear the window when we hit. This discourages people hopping and encourages people to stay in the pool. (unless there is a flaw here that I don't see.