See the discussion of setting a variable with echo in Chapter 11,
“Command-Line Master Class, Part 1,” or the man pages for sysctl and
echo for more.Understanding Computer Attacks
There are many ways to classify computer attacks. Perhaps the easiest way is
to characterize attacks as internal, or computer attacks done by someone with
access to a computer on the local network, and external, or attacks by
someone with access to a computer through the Internet. This might sound
like a trivial separation to make, but it is actually important: Unless you
routinely hire talented computer crackers or allow visitors to plug computers
into your network, the worst internal attack you are likely to encounter is
from a disgruntled employee.
HACKER VERSUS CRACKER
In earlier days, a distinction was made between the words hacker and
cracker. A hacker was someone who used technology to innovate in new or
unusual ways, whereas a cracker was someone who used technology to
attack another’s computers and cause harm. So, by the original definitions,
hackers did good or cool things, and crackers did bad things.
This distinction was lost on the general public, and the term hacker has now
regretfully come to mean the same thing as cracker for most people.
However, we recognize the distinction and use the term cracker to mean a
malicious person using a computer to cause problems for others. In your
real-world conversations, realize that most people do not make a
distinction, and so be prepared to define your terms if you call yourself a
hacker.Although you should never ignore internal threats, you should arguably be
more concerned with the outside world. The big bad Internet is a security
vortex. Machines connected directly to the outside world can be attacked by
people around the world, and invariably are, sometimes even only a few
minutes after getting connected.
This situation is not a result of malicious users lying in wait for your IP
address to do something interesting. Instead, canny virus writers have created
worms that exploit a vulnerability, take control of a machine, and then spread
it to other machines around them. As a result, most attacks today result from
these autocracking tools; there are only a handful of true clever crackers
around, and, to be frank, if one of them ever actually targets you seriously, it
will take a mammoth effort to repel the cracker, regardless of what operating