College students do it. Coffee shop customers do it too. Your neighbor in Apartment 3C is probably doing it right now.

Many computer users search for an available wireless network to tap into -- whether at the mall, at school or at home -- and whether they have permission to use that network or not. Knowingly or unknowingly, these wireless "parasites" may be doing more than filching a signal. When they connect, they can open up the network -- and all the computers on it -- to an array of security breaches.

These problems are compounded when someone allowed to use an organization's wireless network adds an unauthorized wireless signal to increase the main network's signal strength. These unauthorized access points are especially vulnerable, often unprotected by any security measures that may exist on the main network.

At home, people usually use passwords to protect their wireless network from unauthorized access. But a new study by the A. James Clark School of Engineering's Michel Cukier indicates passwords alone may not provide enough protection for home wireless networks and are particularly inadequate for the wireless networks of larger organizations. Cukier is an assistant professor of mechanical engineering and affiliate of the Clark School's Center for Risk and Reliability and Institute for Systems Research at the University of Maryland.

At many organizations and locations around the country, thousands of users access widespread wireless network legitimately at any given time. But in turn, some of these users set up their own wireless networks, linked to the official network, to increase the signal in their office or home -- what computer experts call an unmanaged wireless access point.

"If these secondary connections are not secure, they open up the entire network to trouble," Cukier said. "Unsecured wireless access points pose problems for businesses, cities and other organizations that make wireless access available to customers, employees, and residents. Unsecured connections are an open invitation to hackers seeking access to vulnerable computers."

Cukier recommends that wireless network owners and administrators take the following precautions to better secure wireless networks from "parasites" trolling for access and unsecured connections set up by legitimate users:

* Limited signal coverage. Limit the strength of your wireless network so it cannot be detected outside the bounds of your home or office.

* Turn off SSID broadcasting. A Service Set IDentifier (SSID) is a code attached to packets (bits of information) on a wireless network that is used to identify each packet as part of that network. When SSID broadcasting is enabled on a wireless network, this network can be identified by all wireless clients within range. Conversely when SSID broadcasting is disabled, the wireless network is not visible (to casual users) unless this code is entered in advance into the client's network setting.

* WPA/WEP encryption. Encrypted communication will protect confidential information from being disclosed. If the traffic over the wireless network is encrypted, an attacker must decrypt the password before retrieving information transmitted over the network. There are two encryption schemes available: Wired Equivalent Privacy (WEP) and Wi-Fi Protected Access (WPA). In practice, only one of them can be used at a time. Regular changing of the encryption key may also help to protect the network. Whenever possible, WPA should be used as WEP can be decrypted by hackers equipped with special software.

* Key management. Even if encryption is used, if the key to this encryption (generated by the network) is not changed often, a hacker might crack the key and decrypt the communication. Therefore, the key must be regularly changed.
* MAC address. If a wireless access point only accepts connections from known MAC addresses (essentially a serial number unique to each manufactured network adaptor), a potential attacker will need to learn the addresses of legitimate computers in order to access the wireless network.

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