The Financial Services Authority has discovered that overseas fraudsters are using tactics such as cloning genuine company websites and altering telephone or email details as part of a scam to sell worthless shares.

The FSA on Wednesday revealed that it had been witnessing "dramatic increase" in fraudsters selling shares relying on the names, registration numbers and addresses of FSA authorised firms and individuals.

"It is encouraging that awareness of share scams is now so high that conmen have to come up with new tactics as it shows our strategy is working", says Jonathan Phelan, Head of the FSA's unauthorised business department.

The FSA urges for vigilance and urging the public to report any suspicious, pointing that knowledge of share scams was now so large that conmen had been forced to come up with new tactics.

The FSA, is reported to have estimated that share fraud costs the UK between 150 million and 300 million pounds a year, this month sent warning letters to 10,000 investors whose names appeared on a list used by "boiler rooms" -- unauthorised, overseas-based companies with bogus addresses and phone lines routed abroad.