How do I tell?

If nothing else, your AP/router/whatever should have some way to display the MAC addresses of all the systems that are connected.

That's only if he doesn't want them in.

He just asked if there was a way to see.

There are intrussion detection systems for Windows and wireless networks. But these programs are for professional use and very expensive (>$1000). On Linux the free wireless tool Kismet brings limited intrussion detection functions with it.

There is only one way to watch the network from an other point then the AP. You need to sniff all traffic on the channel. On Windows there are special modified drivers needed to du so, on Linux most wireless drivers have the needed functions biultin or can be patched.

Thomas

Look at AirSnare...

Is there some reason you didn't reveal the make and model of your wireless router? They're not all the same and solutions of this sort tend to be unique to the device. See what fits:

1. Arpwatch for Linux. Detects a new MAC address on the LAN. The Windoze version is WinArpWatch:
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   Search Google for "Wireless Intrusion Detection" systems. There are dozens of varying quality and prices.
2. SNMP. If your unspecified router supports SNMP broadcasts (many Linksys do), then you can use an SNMP watch utility. I use:
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   some other SNMP trap logging software.
3. MRTG and SNMP. I use a MIB browser to extract the number of client connections from an access point and graph the number of connections (and other things) using MRTG. The access point(s) must support SNMP for this to work.
4. Wi-Fi Defense.
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   keep looking at this, but never have time to try it. Your turn.

6.

Security is a good thing, or so I've been led to believe.

Surely it's worth $30. You'll probably spend days testing or writing software just to save a lousy $30. No wonder programming isn't the road to riches. Sigh...

See "Linksys Logging Utilities":

think all of them are free. I still prefer Log Viewer: it's not intended to act as an alarm or security system. You can add your own scripting or log file grovelling scripts to do the actual detection of the added MAC address. Just about any SNMP trap logger, SNMP event logger, or syslog simulator will work.

Sorry, my fault for not mentioning more detail. I have a Linksys WRT54G running 4 computers, soon to be secured via WEP.

Jeff : I tried Wi-Fi Defense and liked it. It's a shame that it's $30 to buy it though.

Does anyone know of any software similar to Wi-Fi Defense that is free?

Thanks.

Hi

If you are using the Router's DHCP, there is a menu in the Router that would show you the IPs that are logged.

If there is an IP that is not used by your computers then someone is leaching.

Be sure to use the security measures just in case:

Jack (MVP-Networking).

Note, however, that someone programming up a static IP can still use your network without the DHCP server's logging showing it. Use the "Show me the connected MAC addresses" function instead of the "Show me who I handed DHCP addresses out to" function.

And yeah, turn on at least 128-bit WEP with a good random hex key.