It is possible to win millions of dollars at an online casino, just like in a land-based casino. Many internet casinos offer progressive jackpot games, which are linked to a network of casinos and can grow to enormous sums of money.
However, winning such large amounts of money is extremaly rare and requires a great deal of luck. The odds of hitting a progressive jackpot are generally very low, and it's important to remember that the majority of players will not win such large amounts.