In this lesson,
we're going to take a look at Trojans.
Now, before we dive into this piece of malware,
let's look at history for a moment
and learn what a Trojan actually is.
Now, a couple of thousand years ago
Greece and the city of Troy were at war.
This lasted for about 10 years with no end in sight.
After a long siege, the Greeks started getting restless
and they decided they were going to try something different.
So they went out and constructed a large wooden horse
that they decided to give to the city of Troy
as a peace offering.
Now, unfortunately, for the citizens of Troy,
this seemingly harmless gift was actually filled
with Greek soldiers,
and once it was wheeled safely into the city,
the day turned to night
and the soldiers came out from within that Trojan horse.
This handful of soldiers then went over
to the walled city's gates, unlocked them and opened them,
and let the rest of the invading Greek army into the city
which rapidly laid waste to the entire city of Troy.
Now, this is where the term Trojan horse,
or as we call it in cybersecurity, a Trojan, gets its name.
Now, in cybersecurity
Trojans work quite similarly to the gift horse
delivered by the Greeks to the city of Troy.
Now, a Trojan is simply a piece of malicious software
that is disguised as a piece of harmless
or desirable software.
Basically, a Trojan claims it's going to perform
some kind of needed or desired function for you
and that Trojan will indeed perform that function,
but it also performs a malicious one
like installing a backdoor or virus
onto your system as well.
Now, when I was a kid back in the 1980s
there was this great new game that came out called Tetris
and everybody loved it.
Now, Tetris was, and still is, an extremely popular game
and everybody wanted to get a copy of it back in those days.
But back then,
we really didn't have the internet to download games,
and so instead, you may have received a floppy disk
from your friend at school who had a copy of the game.
Now, this became a common practice, and back in those days,
people really weren't thinking about computer viruses
the way we do today.
Well, an attacker got this great idea
of embedding some malicious code
into the Tetris game and then passing out disks
with that infected version to lots of different people.
If you received one of those disks,
you might put it in your computer in order to run the game,
And when you did that,
the game would actually play just like you thought it would,
but what was actually happening
behind the scenes was it opened a connection
between your system and their system
so the attacker could gain remote access
and control over your system.
Now, what I just described is one of the earliest examples
of what we now refer to as a RAT, a Remote Access Trojan.
Now, a RAT is a type of Trojan
that's widely used by modern attackers
because it provides the attacker with remote control
of a victimized machine.
Now, let's go back to that Tetris example,
because young Jason found this to be a great way
to mess around with his online friends.
So I could go out and give a copy
of this infected version of Tetris over to my friends,
and when they started playing it,
a remote connection would be created from their machine
back to my machine.
Now, once that connection was established
I could do all sorts of things that I thought were hilarious
on my friend's system, like logging in as them
on their computer, opening and closing their CD drive,
playing music or alerts on their computer,
flipping their screen upside down
so that everything appeared backwards or upside down,
and all sorts of other weird things like that,
all while maintaining remote access and remote control
of my friends' computers by using this Trojan.
Now, in my case, this was being done for fun
against my friend's computers or later on in life,
as part of my network penetration test
that I was involved with over the years.
So remember, when you're dealing with a Trojan
you're dealing with a piece of malicious software
that's disguised as a piece of harmless
or desirable software.
Trojans are commonly used by attackers
to exploit a vulnerability in your workstation
and then conduct data exfiltration
to steal your sensitive documents and create back doors
to create persistence in your system
and other malicious activities like that.
So, anytime you download a program from the internet,
you always need to be careful to check them for Trojans
by using a good anti-virus or anti-malware solution
prior to opening or installing any programs you download,
as well as making sure your systems are patched
against known vulnerabilities
in order to prevent your system
from falling victim to the attacks created by Trojans.