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What Are Leaks?
Host based software "personal firewalls" that fail in outbound application filtering are said to "leak". Trojans and malware will try to establish outbound connections from your computer, whether to download additional malware programs, to send information out to a "home base", or to search for other vulnerable computers to infect. In some cases, the outbound information transmitted is innocuous in and of itself. In principle, if you don't want the information transmitted, it's a problem whether it's harmless or not. Any connection outbound not made by a valid user or process is undesirable and a potential vulnerability.
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What Are Leak Tests?
Leaktests are software applications created to specifically check for methods and means to bypass personal firewall protection. Often the software is a group or suite of tests run in sequence. Usually leak tests are available online as free downloads or via a web interface if the tests can be run remotely. Sometimes the tests can be run by the average user who does not have expert knowledge of computer security. Others are intended for experts and professionals and it would be difficult for the average user to use correctly or to understand and evaluate the results. Some leak tests are performed by professionals to evaluate existing and new personal firewall software and publish the results for public review and comment. They do this both to inform the users, potential users, and to alert the creators of the software that there is room for improvement.
Some are well known and popular among those familiar or expert in computer security. For example, grc.com's LeakTest has been downloaded over 7 million times. You can read more about free security tests in my article: Top 10 Free Security Tests. My advice, if you don't understand the tests, the test results, or how to configure or change your personal firewall software: ask an expert! A false sense of security is a disaster waiting to happen.
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What Should I Do If My Firewall Leaks?
If you find the results show that your firewall fails those tests, you should answer the following questions. Do I trust these results? Do I understand these results? Can my personal firewall software be configured differently to resolve the problem(s)? Can my personal firewall be upgraded and will that upgrade fix any problems? Depending on the answers to these questions, you may consider using a more secure personal firewall software. I recently reviewed Outpost Network Security Suite. Outpost Network Security Suite Pro performed very well in tests by matousec.com as did their consumer product, Outpost Firewall. Comodo Internet Security is the current leader in their firewall challenge (read our review of Comodo Internet Security). Updates, patches, and new versions of personal firewall software come out frequently. Keep yours updated, and help keep your corner of the Internet a litte bit safer!