Scammers swindled about £190,000 from six Northern Ireland residents in less than a month.
Police received six reports of people losing “serious amounts of money” between 18 November and 16 December.
They included a woman from County Antrim who lost £61,000 through an online romance and a County Down man who lost £36,000 in a fake investment.
Ch Supt Simon Walls said scammers “don’t care if it’s Christmas, new year or summer time”.
He said that four alleged scams were reported to police on 18 December. Another was reported the following day and a sixth on 16 January.
The largest sum of money taken was about £64,000.
It involved a woman from County Antrim who spoke to someone she believed represented a major online retailer before being transferred to a person claiming to be from a UK-wide law agency.
She was persuaded to download an app that would keep her money safe, but it resulted in multiple transactions.
“Scammers operate all year round, which is why I can’t stress enough just how important it is to be vigilant at all times,” said Ch Supt Simon Walls.
“Please, be aware of a phone call, or a dodgy email, where something just doesn’t feel quite right.
“Stay on your guard, every day, and do not let yourself be scammed.”