How to Tell if Someone is Lurking on Your Wireless Network
By Mike Boyds
You heard the old saying "were not alone". Well, the same can be said about your Wireless Home Network.
Have you ever wondered if someone else is on your network, with out your knowledge, watching
every site you visit or stealing account information from your GMail or bank account?
Sure you probably went to great lengths to implement and secure your wireless home network,
but any Network Security professional will tell you NOTHING is bullet proof.
While nothing is bullet proof, being proactive with monitoring can catch the un-wanted guest... off guard.
So what can you do to monitor and identify if someone is wondering around on your home
network? You can use some simple tools, when combined, will help you see your Network and
give you a view of who's online.
NOTE: With these tools chances of identifying someone on your network increases, but
will NOT prevent them from gaining access to your Network. Other tools exist than described
in this article, but the goal is to show you the different type of tools and how to use them.
1. Firewall Logs - is a good place to start. If you have a Firewall running on your
Computer or on your router, look for suspicious activity by scanning the logs for anything
out of the ordinary with inbound and outbound traffic.
One method you can use is to look for patterns. For example, if someone was scanning
your computer to see what ports are open, the logs will show continuous activity from the same
IP Address (an intruder's computer) sending a stream of data to many different ports to a single
IP Address or range of IP Addresses.
Obviously, with a smart hacker, they can do many things to cover their tracks, but one
thing is for sure, data must be transmitted to probe your computer, and patterns is one method
to use for spotting trouble on your Network.
2. DHCP Logs - if the unwanted guest is not Network savvy, or security on your router
is not up to snuff, they may be able to drop in unannounced, by receiving an IP Address from
your wireless DHCP server.
You can easily view a list of active addresses by connecting to your router and checking
the DHCP log. For example, on my Linksys router, the log is located in the Wireless MAC Filter
tab, where I can see and identify all active hosts on my Network. But this does not guarantee
that these are the only active PC's on my Network.
Unfortunately, a more sophisticated hacker can get around the need to rely on DHCP. If
they did their homework (you can be sure of that), they probably figured out the range of IP
Addresses in use on your Network, found an unused address in that range and configure their
PC with a static address.
3. Check Who's Connecting To Your Computer - Now that you identified who the trusted
computers are on your network (from the DHCP logs), you can check who is connected to your
computer. To do this, open a command prompt and enter the following command:
a = Displays all connections and listening ports.
n = Displays addresses and port numbers in numerical form.
Netstat is a useful tool that displays network connections (both incoming and outgoing)
on computers. This will allow you to see all IP Addresses that have made a connection to your computer.
Netstat shows you the type of connection (TCP or UDP), IP Address and port number (number
after addresses separated by a colon) for both Local (your computer) and Foreign addresses.