Thousands of UK citizens may not even be aware they are victims
A father and daughter in the US could go to prison if they are found to be guilty of swindling an estimated $70m (£34m) out of more than 150,000 British citizens though a share scam.
These sorts of illegal operations are widespread, targeting thousands of unsuspecting people in the UK, many vulnerable pensioners.
It is rare for the operators of these schemes to be caught.
Even if they are, it is often too late to get your money back.
Here five victims of such share scams tell of their experiences.
MURRAY JONES, 68, CAMBERLEY, SURREY
About three years ago I was contacted out of the blue by a company called Templeton. They persuaded me to buy a tranche of shares in a firm that was involved with biodiesel, which they said had huge growth potential.
The person had an Irish accent and was calling from an 0800 number.
They sent me a confirmation form to sign and I sent £4,000 in a bank transfer to what they said was an account belonging to an escrow agent - a neutral third party - in Florida or California.
They called again shortly afterwards, asking for more money and said they had changed their name to St James Investments.
Over a period of about six months, I "invested" about £28,000, part of my inheritance.
When I became suspicious and demanded more information from them, they stopped calling and my e-mails and letters have been unanswered.
PATRICK McTERNAN, RETIRED STOCKBROKER, WEST SUSSEX
A friend of mine who was then aged in his 80s was persuaded to sell blue chip shares to reinvest in those of companies of which I could find no trace.
He spent about £43,000, only coming to me after he had completed the deal. I knew instantly that he had been conned because he seemed to have more than 160,000 shares - a lot of shares for the amount of money he paid.
Having worked as a stockbroker 30 years ago, it reminded me of the penny share scams when tipsters used to persuade unsuspecting investors to buy defunct companies in the hope of getting their shares moving and making a profit.
I told my friend to take it up with his accountant. Sadly no progress was made in obtaining a refund.
COLIN ARKWRIGHT, 63, SEMI-RETIRED, ANGLESEY
I'm still not sure if I've been scammed or not.
I received a call from Synergy Wealth Investment Solutions last year, who advised me to buy a stake in a small US biotechnology firm called Biomoda, which does have a listing on the New York Stock Exchange.
I knew the risks were high but I thought it was worth a punt for £2,000. I did receive a share certificate and a letter confirming the deal from a US law firm called Handler, Thayer & Duggan and was happy with that.
Some schemes have offered gains from the soaring oil price
Then, less than a month later, I was contacted by someone else at Synergy who told me that Biomoda had invented a vaccine for Aids and that Canada Life Assurance had signed a contract to buy £40m worth of shares in the firm.
They told me that this was insider information and when it was made in public the shares would surge.
They tried to get me to part with an extra £40,000 on that basis, calling me night and day, and even sent me a nasty e-mail. It was all really annoying and I eventually told them not to contact me again.
RON MILLER, 53, ACCOUNTANT, DUNDEE
Last November, the company I work for was contacted by someone calling from Vertex Commodities selling heating oil.
I was the one who answered the phone and when I told them my firm would not be interested, they asked me if I was.
I checked out their contact details and website, which gave the impression the firm had been doing business for 10 or 11 years.
I sent $5,000 to a bank in Hong Kong and at the end of December, I got a call telling me that my investment was worth $11,400.
The FSA warns about boiler rooms on its website
They told me about another opportunity, this time in copper, and I gave them £5,000 to invest.
When I tried to get in touch at the end of January to find out how my investments were doing, my e-mails were not answered and when I called there was a recorded message saying that the number was no longer in use. The website had gone down too.
I contacted the police in Dundee and a lady from Forfar CID came over and told me about the boiler house scams, some run to fund terrorist activities.
ALAN BELL, RETIRED, EASTBOURNE, EAST SUSSEX
In 2006, I was persuaded to invest in two US conglomerates on the basis that their shares were about to soar.
I had just retired and had a few thousand pounds to spare, which I was deciding what to do with.
I spent about $6,480 in total buying shares in a delivery firm called UDS Group Incorporated at $1.39 a share and a stake in Industrial Biotechnology Corporation for $1.30 a share.
Shares in both firms are now worth substantially less than 1 cent.
I never thought it was a scam, I just thought it was bad luck.