A penetration test, when carried out by outside experts, is the best way to establish how vulnerable your network is from a malicious hacker attack.

But while thorough, third-party penetration testing can be expensive and is effectively out of date as soon as you make changes to your infrastructure or as new vulnerabilities that affect it are discovered.

One way to sidestep both of these problems is to carry out your own network penetration tests.

In this article, we’ll discuss both how to do your own security testing and conduct internal penetration testing, and how to find the best third-party service should you choose to hire an outside pen tester.

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http://www.esecurityplanet.com/network-security/penetration-testing.html