What a firewall Protects You From

There are many creative ways that unscrupulous people use to access or abuse unprotected computers:

Remote login

- When someone is able to connect to your computer and control it in some form.
This can range from being able to view or access your files to actually running
programs on your computer.

Application backdoors

- Some programs have special features that allow for remote access. Others contain bugs
that provide a backdoor,or hidden access,that provides some level of control of the program.

SMTP session hijacking

- SMTP is the most common method of sending e-mail over the Internet.By gaining access to a
list of e-mail addresses,a person can send unsolicited junk e-mail (spam) to thousands of users.
This is done quite often by redirecting the e-mail through the SMTP server of an unsuspecting host,
making the actual sender of the spam difficult to trace.

Operating system bugs

- Like applications, some operating systems have backdoors.Others provide remote access with insufficient
security controls or have bugs that an experienced hacker can take advantage of.

Denial of service

- You have probably heard this phrase used in news reports on the attacks on major Web sites.
This type of attack is nearly impossible to counter.
What happens is that the hacker sends a request to the server to connect to it. When the server
responds with an acknowledgement and tries to establish a session,it cannot find the system that
made the request. By inundating a server with these unanswerable session requests, a hacker causes the server to slow
to a crawl or eventually crash.

E-mail bombs

- An e-mail bomb is usually a personal attack. Someone sends you the same e-mail hundreds or thousands
of times until your e-mail system cannot accept any more messages.


- To simplify complicated procedures, many applications allow you to create a script of commands
that the application can run. This script is known as a macro.
Hackers have taken advantage of this to create their own macros that,depending on the application,
can destroy your data or crash your computer.


- Probably the most well-known threat is computer viruses.A virus is a small program that can copy
itself to other computers. This way it can spread quickly from one system to the next. Viruses range
from harmless messages to erasing all of your data.


-Typically harmless but always annoying, spam is the electronic equivalent of junk mail.Spam can
be dangerous though.
Quite often it contains links to Web sites.
Be careful of clicking on these because you may accidentally accept a cookie that provides a backdoor
to your computer.

Redirect bombs

- Hackers can use ICMP to change (redirect) the path information takes by sending it to a different
router. This is one of the ways that a denial of service attack is set up.

Source routing

-In most cases, the path a packet travels over the Internet (or any other network) is determined
by the routers along that path.
But the source providing the packet can arbitrarily specify the route that the packet should travel.
Hackers sometimes take advantage of this to make information appear to come from a trusted source
or even from inside the network! Most firewall products disable source routing by default.
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