Online gambling giant Bet365 has been whacked with a $2.75 million penalty after being found guilty of luring new punters with a false "free bets" offer.

The Federal Court found Bet365, which markets itself as "the world's biggest online company", had misled and deceived Australian consumers with its "$200 free bets for new customers" offer between March 2013 and January 2014.

It found Bet365 failed to prominently display the conditions, which included that, in order to receive the $200 free bet, new customers had to first deposit and gamble $200 of their own money.

Rod Sims, chairman of the Australian Competition and Consumer Commission, which took Bet365 to court, said the offer was aimed at enticing new customers into what the judge called a "web of deception".