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Nessus Scanner | 
Operating Systems: Windows, Mac OS X,
  OpenBSD, FreeBSD, Solaris, and/or other UNIX variants | 
Nessus was a popular free
  and open source vulnerability scanner until they closed the source code in 2005 and removed the free “registered feed” version in 2008. A limited “Home
  Feed” is still available, though it is only licensed for home network use.
  Some people avoid paying by violating the “Home Feed” license, or by avoiding
  feeds entirely and using just the plugins included with each release. But for
  most users, the cost has increased from free to $1200/year. Despite this,
  Nessus is still the best UNIX vulnerability scanner available and among the
  best to run on Windows. Nessus is constantly updated, with more than 20,000
  plugins. Key features include remote and local (authenticated) security
  checks, a client/server architecture with a GTK graphical interface, and an
  embedded scripting language for writing your own plugins or understanding the
  existing ones. | 
Premier UNIX vulnerability
  assessment tool | 
| 
GFI LANguard | 
Operating Systems: Windows | 
GFI LANguard scans IP
  networks to detect what machines are running. Then it tries to discern the
  host OS and what applications are running. I also tries to collect Windows
  machine’s service pack level, missing security patches, wireless access
  points, USB devices, open shares, open ports, services/applications active on
  the computer, key registry entries, weak passwords, users and groups, and
  more. Scan results are saved to an HTML report, which can be
  customized/queried. It also includes a patch manager which detects and
  installs missing patches. A free trial version is available, though it only
  works for up to 30 days. | 
A commercial network
  security scanner for Windows | 
| 
Retina CS | 
Operating Systems: Windows | 
Like Nessus, Retina’s function is to scan all the hosts
  on a network and report on any vulnerabilities found. It was written by eEye,
  who are well known for their security research. | 
Commercial vulnerability
  assessment scanner by eEye | 
| 
Core Impact | 
Operating Systems: Windows | 
Core Impact isn’t cheap (be
  prepared to spend tens of thousands of dollars), but it is widely considered
  to be the most powerful exploitation tool available. It sports a large,
  regularly updated database of professional exploits, and can do neat tricks
  like exploiting one machine and then establishing an encrypted tunnel through
  that machine to reach and exploit other boxes. If you can’t afford Impact,
  take a look at the cheaper Canvas or the excellent and free Metasploit Framework. Your best bet is to use
  all three. | 
An automated, comprehensive
  penetration testing product | 
| 
ISS Security Scanner | 
Operating Systems: Windows | 
Internet Scanner started
  off in ’92 as a tiny open source scanner by Christopher Klaus. Now he has
  grown ISS into a billion-dollar company with a myriad of security products. | 
Application-level
  vulnerability assessment | 
| 
X-scan Vulnerability Scanner | 
Operating Systems: Windows | 
A multi-threaded,
  plug-in-supported vulnerability scanner. X-Scan includes many features,
  including full NASL support, detecting service types, remote OS type/version
  detection, weak user/password pairs, and more. You may be able to find newer
  versions available here if you can deal with most
  of the page being written in Chinese. | 
A general scanner for
  scanning network vulnerabilities | 
| 
SARA Vulnerability Scanner | 
Operating Systems: Windows, Mac OS X,
  OpenBSD, FreeBSD, Solaris, and/or other UNIX variants | 
SARA is a vulnerability
  assessment tool derived from the infamous (at least in 1995) SATAN scanner.
  They ceased development after releasing version 7.9.1 in June 2009. | 
Security Auditor’s Research
  Assistant | 
| 
QualysGuard | 
Delivered as a service over
  the Web, QualysGuard eliminates the burden of deploying, maintaining, and
  updating vulnerability management software or implementing ad-hoc security
  applications. Clients securely access QualysGuard through an easy-to-use Web
  interface. QualysGuard features 5,000+ unique vulnerability checks, an
  Inference-based scanning engine, and automated daily updates to the
  QualysGuard vulnerability KnowledgeBase. | 
A web-based vulnerability
  scanner | |
| 
SAINT Vulnerability Scanner | 
Operating Systems: Linux, Mac OS X, OpenBSD,
  FreeBSD, Solaris, and/or other UNIX variants | 
SAINT is another commercial
  vulnerability assessment tool (like Nessus, ISS Internet Scanner, or Retina). It runs on UNIX and used to be free and
  open source, but is now a commercial product. | 
Security Administrator’s
  Integrated Network Tool | 
| 
MBSA | 
Operating Systems: Windows | 
Microsoft Baseline Security
  Analyzer (MBSA) is an easy-to-use tool designed for the IT professional that
  helps small and medium-sized businesses determine their security state in
  accordance with Microsoft security recommendations and offers specific
  remediation guidance. Built on the Windows Update Agent and Microsoft Update
  infrastructure, MBSA ensures consistency with other Microsoft management
  products including Microsoft Update (MU), Windows Server Update Services
  (WSUS), Systems Management Server (SMS) and Microsoft Operations Manager
  (MOM). Apparently MBSA on average scans over 3 million computers each week. | 
Microsoft Baseline Security
  Analyzer | 
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XCodeExploitScanner | |||
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Havij-Advanced SQL Injection | |||
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Web Cruiser Scanner | |||
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Acutinex Web Vulnerability Scanner |