Hundreds of computer networks operated by Irish businesses, including major financial institutions, are vulnerable to hackers because basic security procedures have not been implemented.
A survey by Deloitte discovered 884 wireless network points on six streets in Dublin city centre.
Of these, just 44 per cent are using basic measures to prevent unauthorised users logging on to the network and intercepting information sent over them.
Irish businesses are increasingly using wireless networking technology to give staff access to the internet and their internal information and applications. Practically all new laptop computers now sold come with the necessary hardware and software to connect to a wireless network.
Wireless networks use radio waves rather than physical wiring so different computers can communicate with each other. As a result it is difficult to contain the signals within a single building.
Last month consultants from Deloitte carried out a "war-walk" on six Dublin streets - Grafton Street, Harcourt Street, Merrion Square, O'Connell Street, St Stephen's Green and Mayor Street in the Irish Financial Services Centre.
A war-walk involves using a portable computer and an antenna to search for wireless networks while walking around.
Software tools freely available on the internet can then be used to gather information about these networks, such as whether they are using encryption to ensure information can only be accessed by authorised parties.
Earlier this week Deloitte re-created the exercise on a Dublin street accompanied by The Irish Times. During a 10-minute walk a number of open wireless networks were detected. The name of one of these insecure networks was that of a multinational financial services organisation that has an office on the street in question.
Colm McDonnell, director of Enterprise Risk Services with Deloitte, said the main concern is that sensitive financial data sent over these networks could be intercepted by hackers or organised criminals.
"Companies not restricting access to their wireless infrastructure are potentially exposing sensitive internal systems and confidential information to outside parties," he said.