IT has been almost 120 years since Heinrich Hertz became the first person to detect and transmit radio waves. Nowadays, just about anyone can transmit radio waves - that is what you do when you set up a home Wi-Fi network.
Unfortunately, almost anybody can detect radio waves, too. Unless you take precautions, someone using a simple portable computer can hop onto your home network or peer into your laptop at a public Wi-Fi hotspot.
Jupiter Research said that 14 percent of Wi-Fi users have logged onto neighbors' networks in the past year, and 30 percent are worried about their neighbors' getting onto their networks. If someone uses your network to commit crimes or cause trouble, like sending spam, there is a chance you can be charged. And because many PC's automatically connect to networks with the strongest signals, it is even easy to connect to a neighbor's network inadvertently.
Whether you are just becoming interested in wireless home networks or have had a Wi-Fi router for years, it is important to double-check your security settings. By activating even the lowest level of security, you will prevent people from accidentally using your Internet access, and by increasing the security a notch or two, you can hold off a concentrated hacking effort.
The trouble is that all this security talk can get confusing, so networking hardware makers often avoid the subject altogether. I recently bought one of Belkin's Wireless G routers, and while the setup using Belkin's Easy Install wizard worked fairly well, I was surprised that the subject of security never came up. The manual's "advanced" settings are full of security options, but the on-screen wizard does not even suggest that you check the manual for further configuration.
If and when you make it to the security part of the manual - Belkin's or any other router maker's - you are greeted by a flood of scary-sounding terms. A typical router sold today can provide three or four types of security, starting with Wired Equivalent Privacy, or WEP. The early form of encryption for Wi-Fi, WEP is now fairly simple to decode and amounts to little more than a "locked screen door," in the words of one software vendor.
WEP can prevent casual snoopers and freeloaders, but will not deter knowledgeable intruders.
"Residential users absolutely flat out plain should never use WEP encryption," said Craig Mathias, founder of the Farpoint Group, a wireless-technology consulting firm. "It is better than nothing, but with W.P.A. available for the same price, why use it?"
W.P.A. stands for Wi-Fi Protected Access, a wireless security system in all newer Wi-Fi routers. Although users need to remember only a single "preshared" passphrase, the actual key codes computers use to access the network change constantly.
"With WEP, the biggest issue was that it was fairly basic; it used a 'static key' structure, so the key to the network was the same indefinitely," said Frank Hanzlik, managing director of the Wi-Fi Alliance, a trade association. With W.P.A. and its newer sibling, W.P.A.2, new keys are assigned with different sessions and transactions. "As a result, it's much more difficult to compromise," Mr. Hanzlik said.
The security is there - it requires only a software update to use W.P.A. even with most older Wi-Fi routers. But Mr. Hanzlik acknowledged that while technically adept users have figured out how to install a router with security, "setup is not as easy for mainstream America."
One method already available is McAfee's new Wireless Home Network Security. Sold separately for $50 or as part of $100 and $150 Internet security bundles, the software takes control of your unsecured router and locks it down, without requiring much from the user. Though the program has a mode that merely automates what you could do by hand, its core offering is a powerful security manager for Windows-only networks that changes the encryption key to your network every three hours, whether you are using WEP or W.P.A.
The McAfee software has some downsides. It works only with certain routers. And if you use Macs or have a Wi-Fi-enabled product like a camera or DVD player, it could complicate, rather than simplify, your situation.
By paying some attention, you can set up reliable security at home. Where it gets trickier is on the road. Public hot spots do not use WEP or W.P.A. security, because the access key would have to be available to everyone, making it useless.
Anyone can easily browse the data that travels from your computer to the public access point if it is not encrypted. You are safe, for instance, if you send data to Web sites that your browser marks with a key or padlock icon - they use "secure socket layer" encryption. The danger is that valuable information will leak into less secure text files, like e-mail and instant messages.
Corporate users who make use of Wi-Fi in airports and hotels generally connect through an encrypted data tunnel called a virtual private network, or VPN. Spies watching a VPN see nothing but gibberish. If you do not have a corporate information technology person at your disposal but want a VPN of your own, you might want to try JiWire's SpotLock.
When you use SpotLock ($50 a year), your data stays encrypted from its origin inside your computer all the way through the public wireless network and onto the Internet. Once it hits JiWire's servers, it is decrypted and directed wherever it needs to go, safely out of range of coffee-shop bandits. This happens in fractions of a second - you do not notice anything. SpotLock, too, is only for Windows PC's.
When Hertz sent his first radio waves into thin air, he did not have to worry about privacy or identity theft. But now the air is full of data. If clever, persevering people are going to try to get at it, it takes a bit of cleverness and perseverance to thwart them.