Nick Leeson: The original rogue trader

Over the past few years, there have been only three cases on a scale to rival this week's suspected fraud at Allied Irish Banks.

The most famous - and the one most often referred to in coverage of AIB - was the case of Nick Leeson, jailed for fraud following the collapse of Barings Bank in 1995.

He went into the red by a whopping �850m ($1.2bn) by trading on Asian markets, after what he claimed was a well-intentioned attempt to cover up losses in a client's account.

Metals and make-up

Less well-known, but financially even bigger was the �1.3bn blown away by Yasuo Hamanaka, a metals trader at Japanese conglomerate Sumitomo.

Mr Young was not fit to stand trial...

Mr Hamanaka, known as Mr Five Percent on account of his share of the world copper market, was jailed for eight years in 1996 after admitting to a 10-year career of unauthorised dealing.

Smaller but spicier was the case of Peter Young, a fund manager at City bank Morgan Grenfell, later acquired by Deutsche Bank.

In 1996, Mr Young was revealed to have bilked �220m from the funds he ran, thanks to a series of unauthorised investments he concealed.

The case returned to the headlines when Mr Young appeared at City of London Magistrates' Court wearing a woman's jumper and dress - and was eventually found unfit to stand trial.

Smaller potatoes

But for the most part, dodgy dealing is a more mundane affair - a few million here, a few million there.

There is hardly a major City name that has not been hit by some sort of trading scandal in the past few years, and most sail through unscathed.

... while Mr Five Percent got eight years

In 2000, for example, NatWest was slapped with a six-figure fine by City watchdogs, after admitting that two of its traders had run up losses of �90.5m.

In the same year, commodities broker Peter Leonard brought down his employers, the Muirpace group, after costing it �32m in trading losses.

And John Ho Park did the same for Griffin Trading, losing �6.2m in a day's trading.

Last year, Merrill Lynch sacked two senior executives for failing to supervise a currency dealer who diverted some �7m in profits to favoured clients.

And so on and so forth.

To err is human...

Even more common, but even more rarely reported, are the cock-ups.

Since the average dealer now sits at a desk straight out of the Space Shuttle - and in many cases is relatively inexperienced and working under considerable pressure - mistakes are inevitable.

In May last year, London's FTSE 100 index dropped by more than 2%, after a trader typed �300m, instead of �30m, while selling a parcel of shares.

In 1998, in the biggest incident of its kind ever, a Salomon Brothers trader mistakenly sold �850m-worth of French government bonds, when he carelessly leaned on his keyboard.

And at the end of 2001, shares in Exodus, a bankrupt internet firm, jumped by 59,000% when a rogue trader accidentally bid $100 for its shares, at a time when its value was 17 cents.

... and increasingly common

All these cases rarely cause the collapse of a firm.

Turbulent times breed fraud and failures

Even Sumitomo, worst hit of them all, survived.

But the bad news is that such incidents could become even more common.

Times of crisis or uncertainty are fertile breeding grounds for fraud and cock-ups: nervous traders make mistakes, and loss-making traders become fraudsters to cover their own tracks.

Ever since the spring of 2001, when the long hi-tech boom came to an end, financial markets of all kinds have behaved with alarming volatility.

Losing money, it seems, just keeps on getting easier.