Free IT Security and Networking Tools
ClamAV is an open source anti-virus toolkit for Unix OS. It is designed for virus scanning on e-mail gateways.
IPCop is a free Linux firewall and VPN gateway for small networks and home users.
My IP Suite is a suite of networking tools for tracing IP addresses, finding out the associated country location and more.
Putty is a free open source telnet\SSH client application commonly used to connect to remote infrastructure devices such as routers and firewalls. You can download Putty for free and use it for other purposes as well. Putty can be used on both Windows and Unix platforms.
Radmin offer a network scanner for windows providing the ability to find all computers on a network.
Shorewall is a free Linux firewall.
Snort is an open source Intrusion Detection Prevention software. This will protect you from various attacks against your clients and servers.
WinSCP is a free SCP client that can be used with Windows OS. One of the most common uses of WinSCP (Windows Secure Copy) is transferring files between Linux and Windows operating systems. An example would be many Windows professional users prefer to transfer files over to Linux using WinSCP because it provides a Windows Explorer like interface.
Wireshark is a network protocol analyser that works on both Unix and Windows systems. Wireshark is a great tool for troubleshooting and other uses such as looking at the TCP connections \ conversations to and from your system.