Many of the wireless networks used by firms in Europe's financial centres are wide open to attack, research shows.
Wi-fi networks are widely used in businesses
A survey by RSA Security found that a third of businesses are still not doing enough to protect data passing over wi-fi networks.
Worst offenders in the survey were firms in Milan which left 72% of wi-fi data broadcast unencrypted.
RSA said lax wi-fi security could leave firms open to a range of potentially damaging hacker attacks.
Wi-fi or wireless networks have become hugely popular among firms in many of Europe's financial districts.
The RSA Security survey found that in London alone the number of wi-fi access points, which act as a hub for a wireless network, has grown by 770% in the last three years.
Despite publicity about the security shortcomings of wireless technology many firms are still failing to take basic steps to protect the data flowing across the wireless nets.
RSA Security questioned firms in London, Paris, Milan and Frankfurt to find out what steps were being taken to keep data secure.
Wi-fi nets in London are among the most secure in Europe
On average more than one-third of the firms it surveyed were not using the basic data scrambling technology built-in to the wi-fi network software.
Italian firms were the least likely to use this basic protection but only 41% of businesses in Frankfurt and 33% in Paris and London used it too.
RSA said that many firms it questioned also seemed to be fitting and forgetting about wi-fi access points.
Many used the default settings that activated when the hardware was first plugged in and switched on.
Again Milanese firms were the most likely to leave default settings untouched. Almost 50% of the access points in Milan used the basic settings compared to 39% in Paris, 33% in Frankfurt and 25% in London.
RSA said that leaving the basic settings intact could act as "bait" for attackers.
"The sheer volume of improperly configured networks across Europe is still concerning and is leaving hundreds of businesses wide open to hacking," said Matthew Buckley, spokesman for RSA Security.
The good news that came out of the research was firms' gradually increasing use of techniques to identify legitimate users and to cordon off the wi-fi network for their own employees.