The term "wireless security" may seem a contradiction in terms. After all, how can any data sent into the open air be secure? Thanks to the advent of digital cell nets and encryption, only mobsters and terrorists really need to worry about phone tapping any more. And few phone conversations have anything in them that would interest a thief. But what about wireless data sent over Wi-Fi networks? Every time you log on to a public Wi-Fi access point, you are transmitting your login name and password over open airwaves, and often a credit card number as well. And given that public networks offer the opportunity for bad guys to capture mountains of such data, it's right to be worried. At airports like O'Hare, there are literally dozens of rogue networks just waiting to entrap unsuspecting travelers.

While individual home networks may not be quite as attractive to wireless hackers, do you really want your neighbor stealing your bandwidth, or passersby snooping around your hard disk? As recently as two years ago, surveys revealed that most public and private Wi-Fi networks used no encryption at all, meaning that anyone with a laptop and Wi-Fi card could intercept and read data packets being sent or received by legitimate users. While more home networks use encryption now, they often use WEP, which is easily cracked. All hackers need are readily downloadable "sniffing" tools, such as those used by "wardrivers." (Wardrivers are those who wander the streets with Wi-Fi gear looking for networks to join -- most are hobbyists or simple bandwidth seekers, but some are malicious.

Home improvement giant Lowe's found this out the hard way, when a Wi-Fi network it was using to transmit credit card and other data from cashiers to a central network was broken into by three college-age men sitting the parking lot of the Southfield, Michigan store. Not only did they capture credit card information, but they actually altered the software code used by Lowe's to process credit cards, and gained access to computers in six other stores as far away as Long Beach, California. Only after Lowe's discovered the intrusion at its headquarters in North Carolina did it call the FBI, which then found the men in the parking lot, followed them home, and arrested them. The men later admitted they had discovered the unprotected network while wardriving earlier in the year.

Lowe's case is not an isolated one. Most such break-ins probably go undetected, unless obvious damage is done. One particularly chilling example comes from Haifa, Israel. A break-in at a post office showed nothing missing, so police assumed the burglars were foiled. But a few weeks later, automated auditing systems showed large withdrawals from newly opened accounts, prompting an investigation. Only after much head-scratching did officials find that a Wi-Fi access point had been added to their internal network, planted innocuously right in the middle of all the other server equipment in a closed area. If the withdrawals had not triggered the auditing program, the scam could have gone on indefinitely.

Another scary case involves the theft of over 2,000 patient records at a clinic in Raleigh, North Carolina. Hospitals often use wireless networks to transmit data from the bedside to central servers. While the culprit here claimed he was only trying to expose the vulnerability of the network, patient records contain everything from social security numbers and credit data to highly sensitive medical information.

Even if you aren't worried about your home network, and don't keep any valuable data on your hard drive, you should still be concerned about bandwidth hijackers. In perhaps the most shocking Wi-Fi crime to date, a man using a laptop in a moving car was found by Toronto police naked from the waist down and downloading child pornography thanks to open Wi-Fi nets in a residential neighborhood. Police only stopped him because he was going the wrong way down a one-way street. Worse, if such downloads are traced back to your IP address, you could be charged with possession of pornography yourself.

So what can you do to make your wireless net safer? Thankfully, the answer is "a lot." While no network is 100 percent secure, you can make your wireless net just as safe as a wired one, and prevent all but the most dedicated and resourceful crackers from getting in. And it won't cost you anything but a little time.

What follows are some down and dirty tips to help you keep your private data private. We've divided them into two sections: how to secure your home Wi-Fi network, and how to be safe when using a public hotspot. Corporate Wi-Fi security is a whole 'nother bags of tricks that we can't cover here, but suffice it to say, if you run a business that uses Wi-Fi, you should be using enterprise-level security tools like RADIUS authentication servers and dedicated Virtual Private Networks (VPNs).