The Financial Services Authority (FSA) is contacting 76,732 people to let them know they are being targeted by fraudsters trying to con them out of their money.
The people's names all appear on a number of lists recovered from companies that the FSA believes were fraudulently selling investments in land or worthless, sometimes non-existent, shares.
The watchdog has compiled all the information into one 'suckers list', which now forms the basis of the largest number of targeted fraud victims the FSA has ever contacted in one go.
The victims will start receiving letters from the regulator today. But in some cases the list only included email addresses so some people will only be receiving an email from the FSA to warn them.
If you think you've been scammed get in touch by leaving a comment below or emailing us on email@example.com and let us know exactly what has happened.
Fraudsters' phone books
"These lists are nothing more than fraudsters' phone books and the people that use them are ruthless, calculated and will stop at nothing to steal your money. A call out of the blue is one of the hallmarks of investment scams, so if you ever get an unexpected call with promises of fantastic returns – you should be extremely sceptical," says Jonathan Phelan, the FSA's head of unauthorised business.
The letter (which can be viewed online here) advises people on how to spot a scam, how to avoid becoming a victim, and what to do if you have already invested in a con.
The FSA has put out an additional warning that it will not follow up the letters with calls for further information and would never ask for money, bank account or personal details. So don't get caught out by a scammer using these letters as a way to get your personal details.
"If you get a letter or email from the FSA over the next five or six weeks, please read it - it could save you tens of thousands of pounds. If you have already been contacted by a firm offering you a "once in a lifetime" investment opportunity or have already invested, then tell us. The information you have could help us catch criminals and shut down their scams," says Phelan.
Given the huge number of emails and letters the FSA needs to send, it will be doing so in waves. The first 10,000 letters will hit doormats today, with a further 10,000 going out each week. The first 5,000 emails will be sent on 30 April, with a further 5,000 each week after that.
If you have any questions about this particular letter or investment scams in general you can contact the FSA on 0845 155 6355.