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Testing Internet Security
Internet traffic from coming into your home network. However, if your laptop
is infected and you plug it into your home network, all the machines become
vulnerable because the threat is now inside your firewall. I go into more detail
about how firewalls work in the next section, but first, test your connection to
see how exposed your computers are to attacks from the Internet and from
other machines on your internal network.
Testing Internet Security
Ports are the gateways inside your computer. When a computer program wants
to communicate with a remote computer, it makes a connection through a
port that it uses to talk with the computer. Each computer has thousands of
ports—65,535 to be exact. You can think of the different ports as a bunch of
different mailboxes. When a program wants to send data to a remote computer,
it sends it to a specific port (mailbox) number. Then, provided that a program
on the remote computer is set up to receive data at a particular port (mailbox),
the remote computer can work with the data it was sent.
Theoretically, nothing is wrong with this scenario. In the real world,
applications don’t always work this way. Sometimes, applications are sent data they
are not programmed to receive. This can cause errors and unexpected behavior
that may execute code a remote attacker is sending it. The result is that a remote
attacker can gain access or infect your computer using a law in the
application. The technical name for data sent to a program that results in bypassing
security is an exploit .
Now that you know the basics of how attacks work, you can use various
utilities to check for open ports that allow other users to connect. In theory, if
you have no ports open, it is next to impossible to break into your computer. To
detect the ports on your computer that are open to the entire Internet, it is best
to use a web-based port scanner. If your computer is on an internal network
and is behind a firewall or router, a software-based port scanner will show you
what ports are open internally.
First, check your external port exposure, which everyone on the Internet can
see. To do this, use a web-based port scanner. Various websites offer such
scanners free of charge. I personally like to use to do my testing. Follow
these steps to test your external connection:
1. Open a copy of either Internet Explorer or Firefox and navigate to http:// .
2. When the page loads, click the Proceed button.
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