Users of some public Wi-Fi networks in places such as hotels, pubs and cafes are being warned they may be at risk of having their personal and financial data stolen by hackers.
It follows the discovery of serious cyber security flaws at ten prominent hotels in Dublin and around the country.
IT security company Smarttech visited the hotels between the end of October and the start of November.
They carried out test cyber attacks on publicly accessible Wi-Fi networks in the premises, using techniques they claim even a novice internet hacker would know.
Within 20 minutes, in all ten hotels, they were able to exploit security flaws on the Wi-Fi networks to access guests' web traffic and sensitive information.
This included email login data, credit card details, Facebook passwords, PayPal account details and online banking information.
In some cases, the engineers were even able to access the data from outside the hotels.
The company has now informed all ten hotels of their findings and has recommended they address the flaws.
It is also warning others to check the security of their networks, because under EU law, it is the duty of the premises owner to ensure their network is secure for customers using it.
The Irish Hotels Federation said it advises that individual hotels should inform their guests of the type of internet access being provided and the nature of security that is in place.
However, the IHF said that Wi-Fi users should, for their part, ensure they have appropriate internet security installed on their devices particularly if carrying out commercial transactions online or entering personal data onto web pages.