Wireshark

If you want to know what is going on on your network or whether some malicious or suspicious software broke in and just started floating around your network, you may want to give Wireshark a try.

Wireshark gives you the real answers based on sensitive data about what is actually happening inside your network.

Wireshark was known for many years as Ethereal, and got renamed due to trademark issues in the summer of 2006. With this tool you can capture your network packets on either wired connections (LAN) or wireless connections (WLAN): PPP/HDLC, WiFi, ATM, Bluetooth, USB, Token Ring, Frame Relay, FDDI, and others (depending on your platform). It supports almost all the leading operating systems in the industry, including 64-bit. The supported protocols list is really way beyond your expectation. The major advantage is that the developers are constantly trying to add all the newest protocols defined. As a bonus, by using GeoIP, with Wireshark you can also include or exclude traffic based on a particular country.

The live capture of your network data can be used for further analysis off-line. You can save the captured data into any of the most popular formats.