I have played about 20k tables Texas Hold'em Double or Nothing and stopped playing after 6 months with a profit of 1000$.
I have met quite a few bots and an experienced player will most likely recognize such bots. However it took a while to realize it and I had to look up the stats in order to see it.
The algorithm the bot used was really simple. In poker terms you'd call the bot-player a rock. He bets when he has good cards and will always go all-in whatever happens after the flop.
You'd think that this algorithm is too simple to be succesful but that's wrong. There are two factors that make this strategy profitable:
1. If you play on low limits the players usually play incredibly aggressive and will nearly always lose a lot of money whenever your bot bets.
2. Even if you have a winrate of only 55% (which is necessary to not make a minus, because you never play for free, there is a fee for each table) you will make profit because of the cashback your online poker provider will give you after each month. This is also why you have to play a lot of tables. The bot played about 800 tables each day, which is insane. However it does increase the cashback and the more you play, the more money will get each month.