LONDON , England ( CNN ) -- You 're sitting in an airport lounge and seize the chance to check your e-mails before your flight departs . You log on and are tempted by a wireless Internet provider offering free Internet access . So , do you take it ? Wi-Fi users have been warned to protect their computers against potential hackers at Wi-Fi hotspots . Security experts warn that hackers may be masquerading as free public Wi-Fi providers to gain access to the laptops of unsuspecting travelers . All it takes , they say , is a computer program downloaded from the Internet , an open access point and a user who has ignored basic security advice . `` The difficulty for travelers is differentiating between a good Internet access hotspot and a rogue , or somebody trying to actually glean credentials from you . The issue is that you do n't necessarily know the difference between a good and a bad one , '' computer security expert Sean Remnant told CNN . In 2008 , AirTight Networks dispatched a number of so-called `` white hat '' hackers to 27 airports around the world to test the vulnerability of their Wi-Fi systems . They found that 80 percent of the private Wi-Fi networks tested were open or poorly protected . The wireless security company also found that basic services at several airports , including baggage handling systems , were vulnerable to hackers . Operators were using Wired Equivalent Privacy , known as WEP , which was found to provide inadequate protection to hackers as early as 2001 . One year after the survey was conducted , CNN Business Traveler met Remnant at London 's Heathrow airport , which was not included in the original survey , to test the potential dangers to unprotected Wi-Fi users . Watch what happened when we took a hacker to Heathrow » . Armed with a laptop , our `` white hat '' hacker took a seat in the crowded departure lounge at Terminal 3 and proceeded to scan the airwaves with his laptop , using a program he downloaded form the Internet called Airodump . `` It dumps everything in the air , '' Remnant explained . `` So if I execute the command to start Airodump , instantly I 'm seeing probably 20 wireless networks with four or five of those having relatively weak server security . '' `` There are several risks just on this screen , '' he continued . `` One is that we actually do n't know whether the public networks are legitimate or not . '' The original survey conducted by AirTight Networks found the most common name for rogue Wi-Fi points was `` Free Public Wi-Fi . '' `` You 'd have no idea if somebody sitting down to a laptop was a casual traveler trying to collect their email from an open port , or actually they were setting up a rogue access point , '' Remnant said . `` Your security guys in the airport are n't going to spot someone doing this because it 's a technical thing , '' he added . Once connected , the hacker would have access to everything on your screen , from passwords , to bank account details , to the contents of e-mails . Do you suspect you 've been a victim of Wi-Fi hacking ? Tell us your story in Sound Off . And it 's not just happening at airports . The rapid spread of Wi-Fi networks to cafes , hotels and even entire cities is providing hackers with more opportunities to ply their trade . Last month , Venice rolled out what is believed to be Europe 's most extensive Wi-Fi network . According to mobile media company Jiwire , there are now more than 273,000 free and pay Wi-Fi locations in 140 countries . The majority can be found in the United States , China , the United Kingdom and France . And most hotspots are located in hotels , along with cafes and restaurants . However , the Wi-Fi Alliance , an industry group that tests and certifies Wi-Fi equipment , says the increased availability of Wi-Fi has not led to a rise in hacking cases . `` We certainly have n't seen any kind of sudden epidemic of hackers in open hotspots or anything like that , '' said the group 's marketing director , Kelly Davis-Felner . She said all Wi-Fi enabled devices have in-built security measures , and all users need to do is to switch them on . The most up-to-date wireless security system is WPA2 , which provides greater protection than its predecessors WPA and WEP . `` If you 're updating Facebook , or checking your personal e-mail or surfing the Web , there 's really no reason at all to worry about using an open network , '' Davis-Felner said . `` Any kind of online shopping or banking or anything that would require you to exchange sensitive data over the airwaves , then we advise people to exercise caution . '' The best way to protect sensitive information is to use a Virtual Private Network , or VPN , which encrypts the data moving to and from your laptop . Kiran Deshpande , president of AirTight Networks , had this advice for travelers : `` Connect only to the networks that you trust . Make sure that your communication is secure , disconnect the wireless when you stop using it , and maintain the list of wireless connections that you use on your laptop so that you do n't accidentally connect to networks that may spring up when you 're traveling . ''
Security experts warn Wi-Fi users to be more vigilant against hackers . Experts say it 's difficult to distinguish between legitimate and rogue networks . Comment: Users urged to protect their networks , use VPN for sensitive data .