People need to be cautious of "out of the blue" emails offering shares or other investments, according to the Australian Securities and Investments Commission (ASIC).
Dr Michael Dunn, director of consumer communication at ASIC, said cold calling complaints had doubled from August to September 2004. He said that more buoyant stock markets may have contributed to the re-emergence of these scams.
"Criminals and con artists, operating from offshore, pretend to be stockbrokers or financial advisers," Dunn said. "They phone or email you with offers of shares or other financial products that may or may not exist."
"We have seen increased efforts by these con artists to swindle previous victims through secondary scams, sometimes even posing as investigators or lawyers acting on behalf of other victims."
While Dunn said the public was becoming better informed about investment scams, he added that scammers were always improving and changing their techniques.
"Once your money has gone offshore it is probably gone forever," he warned. "If you want to invest, deal only with a licensed Australian financial services business. Licensed Australian businesses can easily help you deal in overseas investments if you want, and you have more protection if anything goes wrong."