Scientists in the US have warned users of wireless local area networks (Wlans) to use extra security measures after tests showed how insecure such systems are against hackers.

With Wlans already prevalent in the UK public sector, and set to be given a further kick-start in the private sector thanks to new licenses awarded in the recent wireless broadband Government auction, the extra cost for additional security may prove stifling for some.

University of California scientists at Berkeley found that the standard 40-bit encryption used to 'secure' Wlan data being sent over the new popular IEEE 802.11 standard could be cracked too easily.

The 40-bit algorithm makes up what is called the Wired Equivalent Privacy standard. As the name suggests, this algorithm was designed to make Wlans at least as secure as standard wired Lans.

In some ways it does, but the researchers found that Wlans can be cracked using a wireless PC Lan card on a laptop loaded with 'sniffer' software.

Passwords, credit card details and other sensitive data can be grabbed as they pass through the air between legitimate users.

While Wlans are now more attractive to users thanks to the IEEE 802.11 protocol, which allows data to be transported at up to 11Mbps, the extra security features recommended, including 128-bit encryption and virtual private network 'tunnelling' for connections, may prove too expensive for some.

However, some analysts say that such security problems on Wlans could slow the take-up of such projects until the issues are sorted out.

Industry body, the Wireless Ethernet Compatibility Alliance, claimed the research did not expose anything new. It said suppliers were already working on new standard security measures, but no date for their release has been made public.