Meru Networks is using Wi-Fi signals to "cloak" wireless LANs and make it impossible for hackers to decipher them outside the office building.

"Parking lot attacks" are a widely reported wireless security risk, in which hackers outside the building eavesdrop on wireless LAN traffic that leaks out of the building. Most security systems should prevent hackers from accessing the network or making other active attacks, but there is no way to stop attackers passively recording leaked signals, or to detect them doing it. Hackers can then use this data to assist in attacks, or derive company information.

Wi-Fi LANs with no encryption or running the obsolete WEP system, can also be accessed from directly from outside the building, a technique reportedly used in an attack that retailer TJX $188 million. Although WEP is obsolete, it is still in use for some devices such as handheld terminals and VoIP phones.

Meru's RF Barrier positions four directional antennas on the outside of the building, and four extra access points on the inside of those walls. "RF Barrier works by detecting when the transmission of sensitive data occurs between the client and the access point inside the building, and then using the outside directional antenna to transmit different, innocuous data to the parking lot," said Rachna Ahlawat, vice president of marketing at Meru. "The real data and the innocuous data combine and become useless."

Alternatives to this approach include physically blocking the radio signals, using electrical conductors to make the building into a "Faraday Cage", using metal mesh, or using RF-blocking paints and putting a special film on the windows. "Both approaches are expensive and therefore not widely used," said Ahlawat.

The directional antennas mean RF Barrier signals are only projected outside the building, and have no affect on the wireless LAN within the building. Neighbouring WLANs should also be unaffected, as the system only sends legitimate 802.11 frames on channels that the Meru WLAN is already occupying. The barrier can also be turned off, during periods when the company needs wireless access around the building.

"Our Nokia Wi-Fi smart phones handle sensitive voice calls as well as confidential emails and contact information," said Chris Nowak, chief technology officer at an early user, Chicago-based wholesaler Anthony Marano Company. "With our warehouse adjacent to an interstate highway and other major roads, no one is comfortable with blasting a Wi-Fi signal all over the place. RF Barrier lets us decide exactly where we want to draw the border around the coverage area, and we know that the information stops right here."

RF Barrier will be available in September 2008 for Meru's 802.11a/b/g networks, costing $3,595 (£1,806) for four antennas, four access points, cables and software licences. The company's security portfolio also includes rogue prevention, a policy-based firewall, the ability to block applications such as Skype, location-based policy enforcement and secure remote access points for branch offices.