The FBI and SANS have released a report sighting the top 20 computer security holes [here]. To test your network for free, try this service. [ArsTechnica story]

I performed the test against my firewall, which is running Debian Linux and it didn't have any of the vulnerabilities in the top 20. Debian has a package management tool that comes as part of the default Debian installation. Using the tool you can periodically perform an upgrade with one simple command and Debian will update all of the installed packages. Any packages that have been patched against vulnerabilities will also be updated on the Debian system after an upgrade.
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