How about splitting the Lottery into a draw for "older" accounts and then a draw for "new" accounts. These bots have to

continuously have to re-register "new" accounts to go undetected, so if you split the lottery into 2 separate Lotteries, then

the bots will only be effective in the "new" Lottery and the "old" loyal users can have their own Lottery with much less bots

having a influence on the outcome? The users can even be given a choice, where they want to buy tickets. Just put a little

disclaimer on the "new" lottery that chances are higher that this lottery would be infiltrated by bots.