Wireless internet networks in millions of homes can be hacked in less than five seconds, a study claims. According to new research, a quarter of British private wireless networks do not have a password.

An ‘ethical hacking’ experiment in six cities, using freely available software, found almost 40,000 home wi-fi networks at high risk. Separately, there are concerns about the security of those who use free wi-fi networks offered by coffee shops and other businesses.

The study, commissioned by card protection and insurance firm CPP, highlights a ‘cavalier’ attitude to keeping data safe. According to the findings, nearly a quarter of private wireless networks has no password attached, making them immediately accessible to criminals. To make matters worse 82 per cent of Britons think their network is secure.

The report also found that hackers were able to ‘harvest’ usernames and passwords from unsuspecting people at a rate of more than 350 an hour, sitting in coffee shops and restaurants. Nearly a fifth of wireless users say they regularly use public networks.

CPP fraud expert Michael Lynch, said: ‘We urge all wi-fi users to remember that any information they volunteer through public networks can easily be visible to hackers.