Ethical hacker Jason Hart travelled the main arterial routes of six UK cities using basic freely-available "wardriving" equipment. The aim was to identify networks that broadcast wireless signals excessively into public places.
The results showed nearly 40 000 networks as high risk, opening up the personal data of thousands of individuals to hackers and identity thieves.
The study, commissioned by life assistance company CPP, comes ahead of this week's National Identity Fraud Prevention Week.
Nearly a quarter of private wireless networks had no password protection, making them immediately accessible to criminals. But more than 80% of Brits think their network is secure. Further, hackers can break a typical password in seconds, CPP said.
Only one in 20 knew for certain if their network was used without their permission, indicating that the vast majority remain ignorant of the risk, CPP said.
The study also showed the dangers of accessing the internet over publicly available networks. While nearly one in five wireless users (16%) said they regularly use public networks, hackers were able to harvest more than 350 usernames and passwords an hour by sitting in town-centre coffee shops and restaurants.
The experiment also showed that more than 200 people unsuspectingly logged onto a fake Wi-Fi network in just one hour, putting themselves at risk from fraudsters who could harvest their personal and financial information.
Hart said, "When people think of hackers they tend to think of highly organised criminal gangs using sophisticated techniques to crack networks. However, as this experiment show, all a hacker requires is a laptop computer and widely available software."
This story was first published by Computer Weekly