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Firewalls protect your computer from giving unauthorized access to others, without your consent. But sometimes, there may be some gaps or holes in your Firewall which can invite hackers to breach your Internet Security. One of the common way in which a hacker can penetrate your Internet Security is by exploiting the Open Ports in your Firewall.
Firewalls restrict communication between your computer and the Internet. But sometimes, you might need to adjust settings for some other programs that prefer an open connection. You can make an exception for these programs, so that they can communicate through the Windows Firewall.
In some other cases to let programs work properly, your might need to open up some ports also. All these exceptions, weaken your security and sometimes you are not fully aware of the consequences of the allowing these exceptions.
How to check these Firewall exceptions
There are a few services available on Internet, which allow you to test these exceptions. One of my personal favorites is GRC ShieldsUP!
Shields Up is a port scanning service created by Steve Gibson of Gibson Research Corporation and hosted at grc.com. The purpose of this utility is to alert the users of any ports that have been opened through their firewalls or through their NAT routers. The utility can scan the most common file sharing ports, as well as all service ports (1-1056), and user defined ports, in sets of 64.
We have a great compilation of many such services and products, which can do a great deal to tighten your Internet Security. Check out these Links and Resources on Internet Security.