Technology experts have warned of an increase in criminal electronic attacks on commercial internet sites.
Investigators trace e-mails back to the blackmailer.
There has been a growing trend of activity which disables commercial websites, according to the British National Hi-Tech Crime Unit.
There has also been a recent increase in attacks followed by demands for money.
Typically, the sums demanded by the extortionists are in the tens of thousands of dollars.
The basic criminal technique is to overload a commercial website so that it cannot function.
This is followed by a warning to the victim that it will happen again unless money is paid to the perpetrator.
Experts in the field say there has been an increase in this type of crime in just the last few weeks.
The targets are typically businesses whose revenue is heavily dependent on internet transactions, such as online retailers or gambling services.
Those who say this type of extortion is on the rise do have a product to sell which protects against such attacks, and so would profit from increased anxiety about such problems.
But they say they have had a pronounced increase in interest for their services because of increased levels of attacks.
The British National Hi-tech Crime Unit confirmed that there has been an increase in attacks on commercial websites.
But they did not say to what extent the increase was due attempts to extort money rather than a desire to cause damage for its own sake, a kind of electronic vandalism.
The reported increase in extortion is investigated by tracing the e-mails demanding payment and by following the money trail when a payment is made.
Investigators are unable or unwilling to say where the extortion demands originate, but there have been reports that some of them come from criminal gangs in Eastern Europe.
It is thought that many victims are reluctant to make complaints to law enforcement agencies due to fears of unfavourable publicity which might put off customers or draw further attention to their vulnerability to such attacks.