How to win (and lose) £45m in a few minutes

27/12/2017 | By | Reply More

This week in 2011, we were treated to a day of spectacular proportions and this post relives that moment.


It’s a busy week between Christmas and the New year and once out of the Kempton meeting, we move into a quieter period. But Leopardstown still brings us some quality and is worthy of a look as the week wears on. I’m generally less convinced by other markets but will often trade them if an opportunity presents itself.

The are many big races at Leopardstown this week and one of them is the Christmas hurdle. On the day of the hurdle, the meeting overall,  has prize money that often more than all the other meetings combined. That’s why is a focal point for me.

Leopardstown 2011

The 2011 meeting at Leopardstown and the Christmas hurdle in particular. Will always go down in Betfair history for something went very, very wrong.

The exchange is the epitome of fairness. You lodge money upfront to place your bets and all bets are honoured. With a third party bookmaker there are reasons not to pay out but not on the exchange. On an exchange, you see a price and you can take it safe in the knowledge that it will be honoured.

Christmas hurdle 2011

In a fairly standard race, Voler La Vedette ran home to take the win. There was nothing unusual about the win. But there was something really odd about the market. For most of the race £21m was available to back at good odds. Even as the horse pulled away to stride past the post you could be forgiven for thinking that it should be 1.01 to lay as it strode miles past the post. However is was still available to back at odds of 29, not only that you could do it for incredible amounts of money!

There was so much money that nobody was able to take all that money in-running. ‘Only’ £1.6m was matched, meaning the loser would have to pay out a cool £44.8m to the backers. It seemed too good to be true and unfortunately it was, the market was never paid out.

Betfair did eventually give a rough explanation of a technical glitch that occurred that had been spotted and corrected so it could never happen again. But there wasn’t huge amounts of depth to the explanation, though there were a few plausible theories.

When we looked at the data we could see, honestly by coincidence, that the amount of money that was being offered was the maximum positive value for a 32-bit signed integer. For the less technical amongst you, the maximum amount allowed by some computer systems. Was this the cause? Some really obscure bit of code, a lack of error trapping or a weird database issue. Most likely, but I guess the reason for not offering a full explanation was to avoid future exploits? Since then the API and the infrastructure behind the exchange has changed significantly. So I am guessing that this exploit probably doesn’t exist anymore. But it was a ‘funny’ thing to see.


Everything went into melt-down that day. For the full story, you need to read the full blog posts, but also the forum posts for the race. I’ve listed them all for your enjoyment. It will be a day never to forget!

Here are a full lists of what happened on that day: –

  1. Bet Angel forum posts
  2. Biggest ever loss on Betfair?
  3. How to lay £600m worth of bets on Betfair
  4. £1k account caused £600m of error

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Category: General, Horse Racing

About the Author ()

I left a good job in the consumer technology industry to go a trade on Betfair for a living way back in June 2000. I've been here ever since pushing very boundaries of what's possible on betting exchanges and loved every minute of it.

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