A third of older people who have not yet retired have been contacted about "potentially dodgy" pension products, a survey has found.
Which? said that among the 33% who reported potentially fraudulent pension-related offers, 21% said they had been contacted about investment opportunities and 16% were offered a free pension review, while others were suggested help with unlocking their pension or accessing it early.
Some 41% of these people were contacted in the three months before the reforms began - double the number who said they were contacted in the whole of last year.
Those affected were most commonly approached by telephone (52%), but a third received post (37%) or an email (36%).
The watchdog said people should be on their guard if they were approached unexpectedly, "and think very carefully before handing over any money".
But Which? found just half of those polled (50%) were confident that they would be able to identify a legitimate pension investment and 37% feared they could be tricked into a scam.
Which? is campaigning for the government and regulators to do more to increase awareness and prevention of scams and unregulated investment schemes.
Which? executive director Richard Lloyd said: "Recent pension reforms have given people welcome freedom to access their money as they wish, but this has also made millions of pounds more accessible to scammers.
"Anyone who is approached by a company they're unsure about should do some research into the firm and be careful not to rush into any decisions.
"We want the government and regulators to do more to warn people about these types of tricks and do all they can to stamp out the sharks behind them."
The Which? Consumer Rights website warns that phrases like "one-off investment opportunities", "free pension review", "legal loopholes", "cash bonus", and "government endorsement" should be treated with caution.
Equally, pension-holders should be wary if they are approached over the phone, via text messages or in person at the front door, and should never agree to transfer money abroad.