"I had no idea I was being cheated when I was playing," says online poker enthusiast Tom Broadbent ruefully.

"I then saw other players chatting online about 'Chinese collusion' and people were getting compensation.

"So I asked Pokerstars about it and the next day I got a refund."

Mr Broadbent is one 25,000 players recently awarded compensation after falling victim to Chinese card sharps on the world's largest internet poker site, Pokerstars.

In July of this year, the Isle of Man based company refunded $2.1m (£1.63m) to disgruntled customers and has now pledged to step up its security.

The case is not an isolated one. Previously, Pokerstars refunded $80,000 (£52,000) to players who unwittingly went up against poker "bots" - automatic card-playing software programmes.

In the recent Pokerstars case, a group of players based in China colluded by "going easy" with each other in high-stakes games.

By being less aggressive when other members of their ring were at risk of being expelled from the game, they were able to collectively stay in tournaments longer and win more cash from rival players who were oblivious to the fact they were being cheated.

There are some estimates that around 80% of "players" found on-line are actually bots or people playing in collusion. There's a lot of money at stake, and by applying some simple statistics with multiple players you can ensure that you come out ahead at the expense of more naive and "rule abiding" folk (suckers).

I'm not saying it's a good thing to do, I'm just saying it's obviously going to happen.

One scenario I heard about, but haven't been able to find any definite proof of, is where several players in the game are communicating with each other offline and sharing which cards they have. They then collude to win against the others in the room. Just how this can be proven is beyond me but it does seem a plausible scam.

That is what I meant when I said "playing in collusion".

It can be by phone, IM or simply talking to other players at the same physical location. Provided they use proxies to appear from different locations, you can't tell where they are and you have no real way to tell if players are colluding. The casino's only method to detect it is looking for unusual patterns of behaviour, which is not a very exact science.