1. Nmap
I think everyone has heard of this one, recently evolved into the 4.x series.
(”Network Mapper”) is a free open source utility for
network exploration or security auditing. It was designed to rapidly
scan large networks, although it works fine against single hosts. Nmap
uses raw IP packets in novel ways to determine what hosts are available
on the network, what services (application name and version) those
hosts are offering, what operating systems (and OS versions) they are
running, what type of packet filters/firewalls are in use, and dozens
of other characteristics. Nmap runs on most types of computers and both
console and graphical versions are available. Nmap is free and open

Can be used by beginners (-sT) or by pros alike
(–packet_trace). A very versatile tool, once you fully understand
the results.

Get Nmap Here
2. Nessus Remote Security Scanner
Recently went closed source, but is still essentially free. Works with a client-server framework.
is the world’s most popular vulnerability scanner used in over
75,000 organizations world-wide. Many of the world’s largest
organizations are realizing significant cost savings by using Nessus to
audit business-critical enterprise devices and applications.

Get Nessus Here

3. John the Ripper
Yes, JTR 1.7 was recently released!
the Ripper is a fast password cracker, currently available for many
flavors of Unix (11 are officially supported, not counting different
architectures), DOS, Win32, BeOS, and OpenVMS. Its primary purpose is
to detect weak Unix passwords. Besides several crypt(3) password hash
types most commonly found on various Unix flavors, supported out of the
box are Kerberos AFS and Windows NT/2000/XP/2003 LM hashes, plus
several more with contributed patches.

You can get JTR Here
4. Nikto
is an Open Source (GPL) web server scanner which performs comprehensive
tests against web servers for multiple items, including over 3200
potentially dangerous files/CGIs, versions on over 625 servers, and
version specific problems on over 230 servers. Scan items and plugins
are frequently updated and can be automatically updated (if desired).

is a good CGI scanner, there are some other tools that go well with
Nikto (focus on http fingerprinting or Google hacking/info gathering
etc, another article for just those).

Get Nikto Here
5. SuperScan
TCP port scanner, pinger, resolver. SuperScan 4 is an update of the
highly popular Windows port scanning tool, SuperScan.

If you need an alternative for nmap on Windows with a decent interface, I suggest you check this out, it’s pretty nice.
Get SuperScan Here
6. p0f
P0f v2 is a versatile passive OS fingerprinting tool. P0f can identify the operating system on:
- machines that connect to your box (SYN mode),
- machines you connect to (SYN+ACK mode),
- machine you cannot connect to (RST+ mode),
- machines whose communications you can observe.

Basically it can fingerprint anything, just by listening, it doesn’t make ANY active connections to the target machine.
Get p0f Here
7. Wireshark (Formely Ethereal)
is a GTK+-based network protocol analyzer, or sniffer, that lets you
capture and interactively browse the contents of network frames. The
goal of the project is to create a commercial-quality analyzer for Unix
and to give Wireshark features that are missing from closed-source

Works great on both Linux and Windows (with a GUI),
easy to use and can reconstruct TCP/IP Streams! Will do a tutorial on
Wireshark later.

Get Wireshark Here
8. Yersinia
is a network tool designed to take advantage of some weakeness in
different Layer 2 protocols. It pretends to be a solid framework for
analyzing and testing the deployed networks and systems. Currently, the
following network protocols are implemented: Spanning Tree Protocol
(STP), Cisco Discovery Protocol (CDP), Dynamic Trunking Protocol (DTP),
Dynamic Host Configuration Protocol (DHCP), Hot Standby Router Protocol
(HSRP), IEEE 802.1q, Inter-Switch Link Protocol (ISL), VLAN Trunking
Protocol (VTP).

The best Layer 2 kit there is.
Get Yersinia Here
9. Eraser
Eraser is an advanced security tool (for Windows),
which allows you to completely remove sensitive data from your hard
drive by overwriting it several times with carefully selected patterns.
Works with Windows 95, 98, ME, NT, 2000, XP and DOS. Eraser is Free
software and its source code is released under GNU General Public

An excellent tool for keeping your data really safe, if
you’ve deleted it..make sure it’s really gone, you
don’t want it hanging around to bite you in the ass.

Get Eraser Here.
10. PuTTY
is a free implementation of Telnet and SSH for Win32 and Unix
platforms, along with an xterm terminal emulator. A must have for any
h4×0r wanting to telnet or SSH from Windows without having to use
the crappy default MS command line clients.

Get PuTTY Here.
11. LCP
purpose of LCP program is user account passwords auditing and recovery
in Windows NT/2000/XP/2003. Accounts information import, Passwords
recovery, Brute force session distribution, Hashes computing.

A good free alternative to L0phtcrack.
Get LCP Here
12. Cain and Abel
My personal favourite for password cracking of any kind.
& Abel is a password recovery tool for Microsoft Operating Systems.
It allows easy recovery of various kind of passwords by sniffing the
network, cracking encrypted passwords using Dictionary, Brute-Force and
Cryptanalysis attacks, recording VoIP conversations, decoding scrambled
passwords, revealing password boxes, uncovering cached passwords and
analyzing routing protocols. The program does not exploit any software
vulnerabilities or bugs that could not be fixed with little effort.

Get Cain and Abel Here
13. Kismet
is an 802.11 layer2 wireless network detector, sniffer, and intrusion
detection system. Kismet will work with any wireless card which
supports raw monitoring (rfmon) mode, and can sniff 802.11b, 802.11a,
and 802.11g traffic.

A good wireless tool as long as your card supports rfmon (look for an orinocco gold).
Get Kismet Here
14. NetStumbler
a decent wireless tool for Windows! Sadly not as powerful as it’s
Linux counterparts, but it’s easy to use and has a nice
interface, good for the basics of war-driving.

NetStumbler is a
tool for Windows that allows you to detect Wireless Local Area Networks
(WLANs) using 802.11b, 802.11a and 802.11g. It has many uses:

  • Verify that your network is set up the way you intended.
  • Find locations with poor coverage in your WLAN.
  • Detect other networks that may be causing interference on your network.
  • Detect unauthorized "rogue” access points in your workplace.
  • Help aim directional antennas for long-haul WLAN links.
  • Use it recreationally for WarDriving.
Get NetStumbler Here
15. hping
To finish off, something a little more advanced if you want to test your TCP/IP packet monkey skills.
is a command-line oriented TCP/IP packet assembler/analyzer. The
interface is inspired to the ping unix command, but hping isn’t
only able to send ICMP echo requests. It supports TCP, UDP, ICMP and
RAW-IP protocols, has a traceroute mode, the ability to send files
between a covered channel, and many other features.

Get hping Here