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This tip will show you how to scan your system for Trojans using the built-in netstat utility.
First, go to this site and get a copy of the most commonly used ports used by Trojans.
Next, start netstat and see if any of those ports are open: netstat -a.
You can run netstat from the command prompt or the run box along with a series of arguements as follows:
-a -- Displays all connections and listening ports.
-e -- Displays Ethernet Statistics. This may be combined with the -s option.
-n -- Displays addresses and port numbers in numerical form.
-p proto -- Shows connections for the protocol specified by proto; proto may be TCP or UDP. If used with the -s option to display per-protocol statistics, proto may be TCP, UDP, or IP.
-r -- Displays the routing table.
-s -- Displays per-protocol statistics. By default, statistics are shown for TCP, UDP and IP; the -p option may be used to specify a subset of the default.
interval -- Redisplays selected statistics, pausing interval seconds between each display. Press Ctrl+C to stop redisplaying statistics. If omitted, Netstat will print the current configuration information once.
Now, don't freak out right away if one of the Trojan ports are open on your system. You may have an open application using that port for legitimate reasons. You can cross-check this site to see what ports are commonly used and by what.
Netstat generates a lot of text, sometimes too much to see in a single command window. Type: 'netstat -an >c:windowsdesktoplog.txt' or whatever directory you wish. Netstat will create a text based file insert the results into it. This is handy because you can use your text editing program to "Find" or "Search" for the port numbers in the document.
Finally, you can use this Web site to perform a free probe of your ports to see what is exposed to the public Internet.
This was first published in July 2003