"There's a likelihood that within a short period we'll get a spate of these cases," said Brian Worth, the retired head of Scotland Yard's specialist operations. Copy-cat criminals will borrow his modus operandi, as an earlier generation picked up the techniques of the Tylenol poisoner, who launched a slew of product adulteration cases.
"It's a growing business," said Bill Ilsley, director of crisis management at Kroll Associates, the security firm. The big difference from previous crime waves is that it is driven in part by the hole-in-the-wall. The extorter and victim no longer have to meet to hand over cash.
The Barclays case, which came to light last week, is not the only one to alarm companies. Two weeks ago George Fraghistas, a Greek shipping tycoon, was freed by London police after he was kidnapped and held in a cupboard for nine days while his captors negotiated a pounds 30m ransom. Both cases mark a departure from the technique favoured by extorters - product tampering.
"There are attacks on every day of the year," said Mr Worth, now a private security consultant and writer for Intersec: The Journal of International Security. He added that many turned out to be hoaxes, or started as serious attempts but were dropped when the perpetrators became scared.
The first big victim, in 1982, was Tylenol, the leading American painkiller, which was laced with potassium cyanide. Seven people died in Chicago and the killer has never been found. The company, Johnson & Johnson, saw $500m wiped off its profits before it was able to recover sales with what it thought was a tamper-proof package. But the spikers succeeded in striking again.
The Tylenol case was followed by a spate of similar attempts. Heinz baby food was spiked with glass and razor blade fragments. Mars destroyed 3,000 tons of chocolate bars and saw its profits fall by pounds 2.8m, although the threat turned out to be a hoax. Animal rights activists contaminated shampoo with bleach. Rat poison was injected into Contac cold tablets - by a stockbroker who wanted to affect drug company share prices. And an Aids carrier forced Tesco to channel money to him through its discount cards, or he would contaminate its stocks.
Even if the technique is invented by a disgruntled former employee out for revenge rather than monetary gain, it will be picked up by others looking to get rich. Mr Ilsley notes that the Heinz case was followed by copycat demands for cash from more than 250 people unconnected with the original threat.
While the extorters' "bread and butter" has been the threat to poison a company's customers, kidnapping and letter bombs are aimed at a firm's staff. They also point at different targets. Until now, food processors, distributors and retailers have been most at risk. But no company is safe from letter bombs.
Or other explosives. One criminal threatened to plant a bomb in the foundations of a building, said Mr Worth. And as they become more sophisticated, a car bomb like those planted by the IRA could be attempted.
However, the crooks who try to extort money from companies are not like other terrorists. Extorters tend to be individuals rather than organisations. Ordinary terrorists also crave publicity, while extorters prefer anonymity.
Extorters also differ from other criminals. They have probably never broken the criminal law before. Many are failed businessmen and the crime they plan is a one-off. "It's an armchair crime," said Mr Worth. "They get a seductive sense of power from thinking how they can manipulate their victims."
The self-styled criminal masterminds typically start by sending a threatening letter, often with a sample of the product which they have doctored. Presenting a credible threat is not hard. Poisons are readily available on any high street, and books describing where to get bomb-making materials and how to put them together are easy to find. One, The Anarchist's Cookbook, is available at booksellers.
The victims are usually instructed to reply through the classified advertisements of a national newspaper, or to await instructions. This can lead to a period of evaluation and negotiation. The company tries to get into the mind of the extorter. Is he really serious in his threat? Is there a way to stop him? And will the price for paying him off be significantly less than the damage he could do?
Experts believe that commercial calculation leads a fair number of companies to pay up. The objective, profit, depends heavily on their ability to maintain a reputation for supplying safe products.
Opinion on whether companies should agree to pay is divided. The FBI has a policy of helping kidnap victims' families and employers to make ransom payments, although it tries to use the opportunity to ensnare the criminals. British law enforcement officers lean towards the Government's stance of not appeasing terrorists. Mr Worth quotes from Rudyard Kipling's 1911 poem, What Dane-geld Means:
It is always a temptation to a rich and lazy nation
To puff and look important and to say:
"Though we know we should defeat you, we have not
the time to meet you,
We will therefore pay you cash to go away."
If a company does decide to part with its money, the crook faces his biggest problem: how to collect his gains without being caught. That is when most arrests are made.
The problem for the crook is compounded by the physical weight of the cash they have demanded. Even pounds 500,000 in used notes will fill a couple of suitcases and be too heavy to lift easily, let alone run with.
Enter the cash machine, and other electronic means of transferring money. Armed with a false card, the extorter can demand that an account be credited with large amounts. He can then make withdrawals at times and places of his choosing. The
police do not have the resources to stake out every cash machine in the country for months, waiting for alarm bells to ring when the account is activated.
This technique was first reported in the case of Rodney Whitchelo, an ex-police detective who tried to extort pounds 3.75m from Heinz and Pedigree Pet Foods by threatening to contaminate their foods. He was only caught after police manoeuvred him into revisiting a machine he had previously used, and which was by then under observation.
More successful was a kidnapper who established a chain of accounts in different countries, each with instructions to transfer any deposits to the next immediately. Police were eventually able to follow the audit trail to the final bank account, but by then all the money had been withdrawn in cash.
Security consultants argue that the best policy for companies is defence. General measures, such as video camera surveillance, can make it harder for someone to tamper with stocks, or to plant an explosive. Employees can also be warned to be vigilant, and to protect themselves from kidnapping by varying their routes to work.
But letter bombs are more difficult to block. Spotting them needs attention to little details - grease marks from the sweating of the explosives, the faint smell of almonds or marzipan, a flap left ungummed at one end to allow air in for ignition, a label that has been printed rather than handwritten. X-ray can spot most bombs, but screening the post causes delays that can be expensive for a company if it depends on responding quickly to its customers' letters.
Police success rates in catching extorters are as hard to gauge as the number of cases. Enforcement officials do not like talking about their investigations because of the copy-cat phenomena. They they say their success rate is high, and point to the relatively low incidence of kidnapping for ransom in Western countries. But that could be bravado to deter potential criminals. This month's arrest of a man believed to be America's "Unabomber" came after an 18-year spree of murders, and was only accomplished because his brother saw similarities between the Unabomber's published manifesto and his private rantings.
Police do have some advantages, however. In most crimes, their job is to trace clues after the fact. Corporate terrorism is unusual in that the victim and victimiser are in contact with each other, if indirectly. Most crooks are not foolish enough to use the telephone, which can be traced, but any form of communication can reveal clues, however slender. Perhaps the law's biggest asset is the thing that motivates crooks. "They get greedy," said Mr Ilsley. "And when they're greedy they get careless and make mistakes."