Countdown says increasing numbers of people are receiving scam emails telling them they've won supermarket vouchers.
The supermarket chain said the emails used Countdown's logo and asked recipients to provide personal details, complete surveys, or confirm orders they did not place.
The vouchers on offer ranged from $50 to $2500.
Countdown said people should not give their personal details to anyone claiming to be from the company.
People could check Countdown's scam warning page on its website if they suspected an email they received was illegitimate.