Irish people lost almost €3m in investment fraud in the first eight months of this year.
Gardaí say that in the majority of cases people were duped into investing in cryptocurrency by pop-up ads or by online searches.
Some of these ads appear to be endorsed by Irish celebrities.
Gardaí say that when people enter their details on these sites they are contacted almost immediately by fraudsters who get details that allow them to either take control of their PCs or access bank accounts.
They say aggressive sales pitches are also employed telling people they are once-in-a-lifetime opportunities that must be taken now.
Almost 80% of those who reported investment fraud were aged over 40, with cases recorded by those living in all parts of Ireland.
Gardaí also say there was an increase of more than 60% in reports of investment fraud to the force between January and August of this year amounting to €2.9m.
Last year, the total amount of money lost to this fraud was €3.3m.
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But gardaí say they believe these types of fraud are under-reported due to embarrassment, a desire to protect their privacy, or the false belief among people that their investment may come good.
They are advising anyone offered such investments to research the name of the company involved, take independent legal and financial advice, and not to respond to cold calls or pop-up ads advertising such schemes.
They say those who deal with unregulated entities do not have access to Irish financial protections and compensations schemes, and potential investors with any doubts should check the Central Bank website for details.