Commissioner for Communications Regulation Jeremy Godfrey has said it can be hard to tell the difference between genuine calls and scam calls.
Speaking on RTÉ's Morning Ireland, he warned that there are criminal gangs operating overseas and dialling numbers at random to try to scam people.
Mr Godfrey said some come up with stories "that are sometimes very amateurish and sometimes more plausible".
The advice is you do not have to answer calls from unrecognisable numbers. Secondly, do not give out personal data and do not transfer money or bank account details.
Mr Godfrey said if people think the story is plausible check by calling the official number of the organisation that the person says they are calling from.
He said if people think they have been scammed, then notify the gardaí by calling your local garda station and they will give you advice.
"To be on your guard, be vigilant and if someone calls out of the blue and asks for information don't give it to them," he said.
He said Irish people travel overseas and call back home so there are genuine numbers from overseas.
Reflecting on the responsibility of telephone operators, Mr Godfrey said if they notice a pattern in the calls from particular numbers or a surge they can liaise with Comreg and gardaí, who can investigate and try to take action.
