This month, my “At the Airport” column in USATODAY.com is all about airport Wi-Fi.

And all about why more and more airports, including those in Denver, Pittsburgh, Orlando and, just recently, Seattle and Boston, offer this welcome amenity for free – and why some don’t.

Here’s an edited version of that column:

Free Wi-Fi was on Sea-Tac’s to do list for years, but the airport had to wait until its contract with AT&T ran out before making the service free. “It’s almost become a required amenity,” says Sea-Tac airport spokesperson Perry Cooper, “Passengers expect it now. Especially in places like Seattle where folks are very tech-savvy. In fact, it’s been our number one customer service request for years.”

Silicon Valley’s Mineta San José International Airport started offering the service back in May 2008, says airport spokesperson David Vossbrink, because “we serve a high proportion of business travelers and road warriors who have laptops and mobile devices surgically implanted and [they] expect to be able to always be connected.”

It’s pretty much the same story across the country. Everyone wants to stay connected and everyone wants the Wi-Fi at the airport to be free. But how can airports afford to make it free?

Advertising and sponsorship may be the way to go.

At Denver International Airport, which began offering free Wi-Fi in November 2007, between 6,000 and 8,000 travelers now sign on to the system each day and revenue from advertisers help offset the cost of the service. Sea-Tac Airport has asked Clear Channel, which already sells advertising space throughout the airport, to find additional ads to support the new, free Wi-Fi service as well. And at San Francisco International Airport, advertising is being considered as negotiations get underway to figure out how to support a free Wi-Fi program as well. If they can figure out how to fund it, representatives from Nashville International and many other airports say they’d offer travelers free Wi-Fi as well.

Like LAX and the airports in the New York and Washington, D.C. areas, the Minneapolis-St. Paul International Airport still charges passengers for Wi-Fi access. “We know many travelers would love to see free Wi-Fi,” says airport spokesperson Patrick Hogan, “The bottom line is that airports like MSP must generate the funds to cover all airport operating costs…There is no such thing as free airport Wi-Fi. It’s really just a question of who pays to cover the cost of providing the service.”

For the full posted version of this column, read Free airport Wi-Fi takes off in USATODAY.com. And if you’re want to know which airports currently offer free Wi-Fi, the folks at Jaunted.com have been keeping a good tally on their free airport Wi-Fi map.

And if you do use a free Wi-Fi service at an airport, a hotel, a coffee shop or somewhere else, the Wi-Fi Alliance encourages you to use a personal firewall, make sure you have anti-virus software, and keep these other safety tips in mind:

• Make sure that you are connecting to a legitimate hotspot – those that require a password have more protection than those that do not.
• Use a virtual private network or VPN, which establishes a private connection across the public network. This may be supplied by your employer, or you can purchase one.
• Surfing the web and sending e-mail is fine, but doing your banking for example in a public hotspot is not advised.
• Configure for approved connections: Many devices sense and automatically connect to any available wireless signal. To regain control, simply configure your device to not automatically connect to an open network without your approval.
• Disable sharing: Your Wi-Fi enabled devices may automatically open themselves to sharing / connecting with other devices. File and printer sharing may be common in business and home networks, but you can avoid this in public networks.

Got that?

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