A British grandmother won more than 500,000 US dollars the first time she visited an online casino, she said today.

Karen Gibson, 48, won the equivalent of around £285,000 with only her second 3 dollar bet on a virtual slot machine.

The cafe worker, who has four children and four grandchildren, did not realise just how much she had won as she did not know the exchange rate.

She said today: “I was totally bored and was looking at holidays on the internet when the 888.com advert popped up.

“I thought I would have a little go.”

She then registered with the online casino, bought 50 dollars-worth of credits and played the Millionaire Maker “slot machine” which costs 3 dollars a spin.

And on her second spin, she won 503,698.38 dollars – a randomised computer-generated jackpot funded by players all over the world.

Mrs Gibson, married to driver Brian, has barely eaten since she hit the jackpot on Friday night.

She has not decided if she will give up work but will not be moving from her two-bedroomed bungalow.

The couple are keen on holidaying and will look after their children aged 27 to 16 as well.

But she has few other spending plans as her good luck is still sinking in.

She said: “I just cannot believe it.

“I’m sure the kids will all buy new cars.

“They have always come to us for money over the years and I’ll see the joy of them spending it.”

The Middlesbrough FC fan, who lives in the North East, was presented with the mammoth cheque by her favourite player Jimmy Floyd Hasselbaink and his strike partner Mark Viduka at the club’s training ground today.

The impressed Dutchman passed on her congratulations, adding: “We’re going to have to have to get online.”

Viduka said: “Congratulations, don’t spent it all at once.”

Matt Robinson, marketing manager for 888.com, said Karen was the biggest female online winner.

He added: “We see winners as good news and quite simply, the bigger the better.