From Antivirus to
Zero-day exploit:
20 cybersecurity terms you need to know

Cybersecurity touches everything we do online and now more thanever, online life is normal life. By extension, cybersecurity threats are
threats to our livelihoods and educating ourselves is essential for
protecting our wellbeing. Everyone benefits from understanding
the basics which is why the A-Z of cybersecurity terms is important
for all of us to understand.
Troy Hunt
Advisory Board Member at NordVPN, a Microsoft
Regional Director and Most Valuable Professional
awardee for Developer Security, blogger attroyhunt.com, international speaker on web security
and the author of many top-rating security courses
for web developers on Pluralsight.

Foreword
If you’re taking your firststeps into the realm ofcybersecurity, this is theplace to start. To explain
why, let’s see how
things usually work.
You’ve come across the word spyware, and you want to knowwhat it means. The moment you start looking, you’re assaulted byterms you’ve never heard before. You may find a definition like this:Spyware is a type of malware that monitors the victim’s device toextract sensitive data without the victim’s knowledge. Examples of
spyware: adware, keyloggers, and trojans.
That’s an accurate definition, but it’s not super helpful. Now you
have more questions. How does spyware work? What is considered sensitive data, and how worried should you be about its
security? What’s a keylogger? Is that even a word?
We’re taking a different approach.
Rather than giving technical definitions, we’re going to show how
cybersecurity affects your life and provide down-to-earth comparisons. This is not a comprehensive glossary, and it’s so by design.
It’s meant to whet your appetite for further learning.
If you’re looking for more detailed, technical explanations on all
things online security, try our blog at NordVPN.com/blog, which
provides both popular and in-depth content.

Table of contents:
3

Antivirus

4

Botnet5

Ciphertext

6

Data breach7

End-to-end encryption

8

Firewall9

Hacker11

IP address

12

Cryptojacking

13

Keylogger

14

Logic bomb

15

Man-in-the-middle-attack

16

Network

17

Phishing

18

Ransomware

19

Social engineering

21

Two-factor authentication

22

VPN

23

Wi-Fi

24

Zero-day-exploit

A
Antivirus
You got a new email. Subject: I love you
In it, you find a beautiful confession of lovefrom an anonymous admirer. And there’s aphoto too. Curious, you click on theattachment — and download a virus.
Your antivirus immediately quarantines it. You got lucky — it wasan old virus, its signature already in the database.
If the virus is new and not registered in the database, the antivirus
can use other tools to detect it. It monitors your computer for
suspicious activity. If a program tries to bypass the antivirus, runs
on startup without permission, or downloads other malware, theantivirus reacts.
And it’s not only viruses. There are all kinds of malicious software— trojans, ransomware, keyloggers, etc. — that try to compromiseor abuse your devices.

Today, the word
“antivirus” stands in for all
kinds of anti-malware
tools that protect devices
from malware.

Related terms: virus, malware, anti-malware software,
trojan, worm, adware.
3

B
BotnetYou open your browser, enter the address of your favorite meme
website. Awww, it’s down. And you’ll never guess why.
It’s zombies.
Bots, to be exact. A swarm of mindless, infected devices havesent hundreds of thousands of requests to the website andoverwhelmed it.
This attack is called DDoS, which means distributed denial ofservice. People use botnets for this and other nefarious purposes,
like email spam or creating fake internet traffic.
Your devices may also be part of a botnet, secretly responding tocybercriminal’s commands. It’s hard to know whether yourcomputer is a bot — the only sign may be a slightly worse
performance or overheating.

Related terms: bot, zombie, DDoS attack.
4

C
Ciphertext
You open a messaging app and text, “SORRY GUYS, can’t makeit tonight. Probably caught a stomach bug.”That’s called plaintext. It’s unencrypted text that can beintercepted and read by an online spy. That’s also called a lie —you feel fine, but you’d rather watch a movie.
At least you’re using a secure messaging app. It applies analgorithm to turn your lie into ciphertext:“ueEeQrwrd1GL24HWDi2ttNg5fIUXUzqslFqb94^Ef2NU1NBrD
rPb84wbReVnclTP2AgnMCkhaHC3UrfR8VWxh3jWWh+0WE”
That’s encryption in action. Plaintext is turned into ciphertext via
a secure key (a cipher). The messaging apps your friends use havethe key that deciphers your messages. Online spies don’t havethe key and can’t read your communications.

Related terms: encryption, cipher, plaintext, decipher.
5D

Data breach
You have a group chat with a bunch of your closest friends. One
day, you notice screenshots from the chat circling all over social
media. You’ve just experienced a data breach.
A data breach happens when sensitive data falls into the hands ofsomeone who has no business handling it.
How did this happen? A hacker intercepted your communications? Or was it an inside job? Perhaps Mark’s roommate
accessed the chat while Mark was away from the laptop. He
always looked shady. You’ll probably never find out.
That’s what happens in major corporate data breaches too.
Companies collect vast amounts of data — sometimes data fromusers like you — and some of these companies get breached, thedata is leaked, and you see your logins and passwords floatingaround the web.
Periodically check whether your accounts have been compromised in a data breach on haveibeenpwned.com.

Related terms: unintentional information disclosure,data leak, data spill.
6

E
End-to-end encryption
You’ve heard it said in a joyous
tone: “We’ll be implementing
end-to-end encryption!” What’s
so end-to-end about it?
Think of your data as a paper note. Before sending it out, you put
it in an envelope, which protects its contents from eavesdroppers.
That’s encryption.
Somewhere along the way, a third party (for example, the instantmessaging service you’re using) opens that envelope, takes out
your data, and sends it to the final destination.
That’s just how the internet works — there are middlemen all theway down.

End-to-end encryption cuts
out the middleman. Only
you and the person you’resending the note can see its
contents.

Related terms: ciphertext, plaintext.
7

F
FirewallYou’re standing in a line.
When you reach thebouncer, he says, “Noentry.” You turn backand head home — noclubbing today.

The bouncer enforces the rules on who gets into the club andwho doesn’t. These rules are arbitrary — they depend on the
club’s policies and external circumstances. For example, the clubis full, or it’s hosting a private party.
In the same vein, a firewall stands between your local networkand the internet. Like a digital bouncer, it enforces the rules on
which traffic is good enough to enter your network.
A firewall allows traffic fromtrusted sources or IP addresses.
Not on the list? Sorry, traffic,
turn back and head home.
That’s how a firewall protects
your network from malicious
internet traffic that could
compromise your system.

8

H
HackerYou’ve met them in movies. Mysterious, dangerous, even anti-social. They’re digital outlaws who live off the grid. They hack thePentagon in under 5 minutes.
That’s clearly fiction. Hackers are people — and every person has
their motives. Some enjoy the intellectual challenge of breaking
into networks. Others, the so-called black hat hackers, act withmalice. They compromise systems for personal gain, steal valuable
data or money, disrupt networks, and may cause all kinds ofdamage.
Many companies and governments employ white hat hackers,
who test the security of their computer systems by trying to breakin. That’s called penetration testing, which can take many forms —even physical.
For example, a white hat hacker may enter the company
building by following an employee. People are polite — theyusually hold the doors open for others, evenstrangers. Once inside, the hacker
may steal hard drives withsensitive data, access
unsupervised computers or compromise them(with keyloggers,
for example).

9

Can you get hacked?
It depends on your security measures. However, extremely skilled
hackers often find a way into the most secure networks. The
good news is that they probably have juicier targets on theirmind than your Steam account.
Usually, you suffer from hackers indirectly, see: data breach.
What you should be wary of are scammers who set up fakewebsites and send malicious links, see: phishing. Enter yourpassword on a scam website — and you’re giving it directly tothe scammer.
Related terms: grey hat hacker, black hat hacker,
white hat hacker, penetration, penetration testing.
10

I
IP addressYour phone has an IP address (short for internet protocol
address) assigned by your network. So does your laptop, smart
TV, and other every gadget that connects to the internet. No
device could function online without one. Why?
Let’s say you need to kill some time. You take out
your phone and type in “Reddit.com” in theaddress bar.

But your phone doesn’t know what “Reddit.com”
means. Numbers, not words, are its native language. To
access Reddit, your phone sends out a question: “Whatis the IP address of Reddit.com?”
What is the IP address of Reddit.com?

The question is addressed to a
special server — a database of IP
addresses. The server finds Reddit’s
IP and sends it back to your phone.

Reddit’s IP

RequestYour phone then sends out the request
to Reddit’s IP address. Reddit sends
back the information to your phone’s IP.
Reddit’s IP
information

A second passes. Reddit loads on your screen. Meh,nothing sparks your interest, you hit the close button.

11

J
Cryptojacking
Your computer is hot
and buzzing, the fan isspinning like crazy.
And it’s slow — you
have to wait a while
before anything loads.

The reason? A hacker
has hijacked yourcomputer to mine
cryptocurrency.

You’ve probably heard of cryptomining. To put it simply, it’s when
you receive cryptocurrency as a reward for running complex
calculations on your computer. But these calculations take up a
lot of computer power — usually too much power for cryptomining to be profitable.
To solve this problem, hackers hijack devices to mine cryptocurrency for them. They perform this attack — called cryptojacking— by using malware or malicious code in web pages.
Unsuspecting victims are left to wonder why their computer is
red hot from overheating.
P.S. Yes, we know that putting cryptoJacking under J is cheating.
But the letter J is an empty desert when it comes to cybersecurity terms, so we abused it.

Related terms: cryptomining, malicious cryptomining.
12

K
Keylogger
You’re in the library, writing apaper for your economics
class. It’s due yesterday. Your
laptop battery dies,and you’ve
left the cord at home.

A friendly-looking girlis sitting nearby. You ask for her laptop — you need 5 minutes tofinish the thought while it’s still bubbling in your head. She’s glad
to be of help. You take her laptop, log into your cloud drive, andfinish the critique of Depression-era antitrust policies.
When you get back home, you find that your email and a lot of
your online accounts have been hacked. How?
The girl had a keylogger installed on her laptop. It’s a tool that
registers keystrokes. It recorded everything you typed, including
your cloud drive password and login.
Since you use the same password for your cloud drive and email,the hacker gained access to your primary email account (that’s
why you shouldn’t reuse passwords). With it, she reset the
passwords of your other accounts.
Keyloggers rarely come from friendly-looking girls. Usually, theytake the form of hardware gadgets that hackers attach tounsupervised computers. They can also be software tools, usedboth illegally or legally. For example, some corporations install
keyloggers in their computers to monitor their employees.

Related terms: spyware.
13

L
Logic bomb
You're at work, five minutes past a deadline. You’re typing furiously
when everything crashes. You can’t access the internal network or
any remote files. No more work today.
The next day, you hear rumors. It was a former employee, adisgruntled IT guy — he shut down the internal network. But how
can that be? He was fired half a year ago and had no more accessto the company’s systems.
Well, on his last day at work, he left a logic bomb. It is a piece ofmalicious code that activates when certain conditions are met.
For example, when the CEO logs into a sensitive system. A logic
bomb can take effect on a specific date —as happened in our story when the
logic bomb exploded six months
after being set up.

Related terms: time bomb, insider threat.

14

M
Man-in-the-middle attack
You’re in a coffee shop, connected to the public Wi-Fi. You’ve
just sent an email to your contractor, asking for their bankaccount number. You get the number, pay the fee, drink
the flat white.
Two days later, thecontractor calls
you with aquestion: “Whenwill I get paid?”
What?
Flashback to the coffee shop. A hacker arrived at the coffee shop
before you, set up an evil twin hotspot, and named it “Coffee
shop FREE wifi.” Believing it’s a legitimate network, you connected to it. From that moment on, the hacker could monitor yourinternet traffic.
That's a man-in-the-middle attack in action.
The hacker intercepted your email and sent you his own bankaccount number. He got paid, while the contractor is still waiting
for the fee.
Keep in mind the public Wi-Fi is not a safe network. Even if it’s
not set up by a hacker, you never know how well it’s configured. A
man may be lurking in the middle of your communications. Make
sure you use a VPN before connecting to one.

Related terms: evil twin attack, Wi-Fi honeypot.
15

N
NetworkYour devices are a part of a network, which is a part of a bigger
network, which may be a part of an even bigger network, which —you get the idea. That’s the internet, a network of computer
networks, big and small. And you’re on it.
The network that’s closest to you is called LAN — local area
network. It refers to a group of interconnected devices in one
physical location. So when you connect to your home router, youconnect to your LAN.

Your home network is probably quite small, up to 10 connected
devices (or if you love gadgets, a lot more — but we’re not judging,tech is awesome). A LAN can also be company-wide, or it cancover the whole school with thousands of interconnected devices.

Related terms: internet, LAN.
16

P
Phishing
You get an email from your bank. It’s a warning — someone tried
to withdraw money from your account. “Please send your login
and password IMMEDIATELY to confirm your identity,” the banksays.
Sounds scary, but you shouldn’t act out of fear.
Carefully check the sender and you’ll probably find it’s not yourbank, but someone impersonating it. Do not reply, do not click on
any links in the email. Call your bank directly and ask about theemail.
The scam is called phishing and takes on many forms. Messages
or emails that use fear and urgency to extract confidential details.
A fake website that looks almost exactly like your university’s.
Enter your login and password and you’re giving them away to a
scammer.
The defense is simple — be cautious. Be wary of fishy messages
that play on your fears or even worse — promise something too
good to be true. By the way, you’ve
a click here to claim them.

Stop, think, anddouble-check. Do not
click on a link if the URL
doesn’t look legitimate.
As a general rule, neverenter or disclose yourpassword unless you’re
absolutely sure it’s safe.

17

R
Ransomware
You turn on your computer and — wait, what’s this? The screen
does not load. But there’s a message: “Your files have been
encrypted by NarutoRun Hacker Group. You have one week totransfer $500 in Bitcoin to our wallet, or your files will be gone
forever. Rasengan!”Sounds like a plot of a poorly written comedy, but it’s no laughing
matter. Ransomware is a type of malware that forcibly encrypts
the victim’s data. Nobody but the hackers can undo the encryption because only they hold the key. (There are plenty of encryption protocols that are practically unbreakable without thedecryption key. See: ciphertext, end-to-end encryption.)
You shouldn’t pay the ransom because your dollars (more likely —cryptocurrency, usually requested by hackers) would only
support criminals. Instead, learn how to fight ransomware:

Don’t download anything from suspicious websites. Don’t
open suspicious links, emails, or messages. See: phishing.
Back up your mostsensitive files.
Use strong passwords.

18

Update your apps and software,
especially your security software.

S

Social engineering
You are woken up by your phone in the early morning. The personon the other end politely explains he’s a technician at LiteNet,
your internet service provider. They have experienced a network
failure that may have resulted in minor data loss.
Could you provide that last four digits of your credit card number,so that they could match them with the records on their servers?
Half asleep, you do so and get back to your dreams. You properly
wake up two hours later, eat a huge breakfast, and find thatyou’ve been hacked.
The person who called you was no technician, but a social
engineer — a scammer who uses psychological manipulation totrick people into performing a specific action or revealing
sensitive details.

19Let’s break it down. The scammer caught you early in themorning, introduced himself to alleviate your suspicions (LiteNet
is the biggest internet provider in your area, it was an easy guess),and dropped some meaningless technical jargon to soundlegitimate.
Then he called LiteNet pretending to be you and said he’dforgotten his password. He provided the last four digits of yourcredit card number to confirm identity (that is — your identity)
and reset your LiteNet password — including the password foryour LiteNet email account.
LiteNet is a fake internet provider we created for this story. But
many real companies may reset your password over the phone
based only on the last four digits of your credit card. You should
provide as little sensitive information as possible when signing up
and explicitly state not release any details over the phone.
Social engineers employ a lotof techniques to manipulate
users, sophisticated andblunt. A scammer may sendout a thousand fake emails
hoping to find a few victims
that are gullible enough toreply with their credit card
details or passwords. See
also: phishing.

20

T
Two-factor
authentication
You’re logging into
Twitter on your friend’s phone
because you left yours at home. Since this is a new device, youneed to confirm the login on a special authentication app.
Which is on your phone. Which is at home.
Aargh, it’s cybersecurity catch-22!
Yes, it may cause you slight inconvenience, but two-factor
authentication (2FA) secures you with a second layer of protection. If you have trouble accessing your account without yourphone, so will the hackers.
The two factors usually are:Something you know (a password or a pin code).
Something you have (a phone, a codebook, or your biometrics).
No system is impregnable, but 2FA upgrades the security of youraccounts to a level beyond what most users have. Cybercriminals
are usually opportunistic, so instead of trying to work around
2FA, they’ll choose other targets, preferably someone who uses
ABCDEFG as their password.
You should enable 2FA on all services that support it. It’s an easy
way to be much more secure online with minimum inconvenience.

Related terms: multi-factor authentication.
21

V
VPN
You browse, you scroll, you surf. And every time you go online,
you leave bits of data about yourself. Your internet service
provider has access to your online traffic. Every website you visit
can see your IP address.
It’s not just privacy, but your online security that’s also at stake. A
lot of websites still do not use a secure communication protocol.
Most apps do not disclose what kind of cybersecurity practices
they employ. You’re left with having to trust them without
grounds to do so.
A VPN (virtual private network) is a tool that directs all your traffic
through a secure server, encrypts it in the process, and changes
your IP and virtual location. Even though it may sound technical,
VPN is a mainstream tool that’s easily accessible for laymen.
It doesn’t mean that all VPNs are equally good. A VPN routes all
your traffic through its servers, so it may collect your data and sell
it to the highest bidder. The good news is that most of thebiggest VPNs are transparent about their practices, keep no user
logs, and so have nothing to sell or disclose to third parties.
For example, we at NordVPN have our no-logs policy and service
regularly assessed by a Big Four auditing company.

Related terms: time bomb, insider threat.
22

W
Wi-Fi
You’re in your hotel room, browsing on the free Wi-Fi. A few floors
down, a hacker is spying on your online activity. How?
Public Wi-Fi is inherently unsafe — cybercriminals can use manymethods to exploit or compromise it.
If the router is poorly configured, a hacker could observe theinternet traffic of anyone using the public hotspot. Or the hacker
may find a way to inject malware over the network into yourdevice.
A hacker may set up a fake hotspot — an evil twin — and trick you
into connecting to it. See also: Man-in-the-middle attack.
How safe you are depends on:
The configuration and security measures on the hotel Wi-Fi.
The security practices of websites you visit and apps you use.
Your personal cybersecurity practices.
Usually, you can’t know how secure a public network is, so avoid
accessing sensitive data when connected to it. Why not switch tomobile data instead? Or turn on a VPN?
P.S. If you’re organizing an event, don’t rely on the Wi-Fi provided
by the venue because it’s rarely secure. Properly setting up a
Wi-Fi hotspot is no easy task and requires precise technicalknowledge — better hire professionals if you don’t have thetechnical skills.
But your job is just as important — you need to communicate!
Inform the attendees of the event about the official hotspots andwarn them not to connect to any other hotspots, even if they
seem legitimate.
Related terms: malware injection, Wi-Fi sniffing.
23

Z
Zero-day exploit
You updated your software, installed anantivirus, turned on your firewall. At this moment, no hacker could break into your system, right?
If only it were that simple.
Computer networks, software, and hardware are created bypeople. People make mistakes, they do not think through every
possible scenario, they leave vulnerabilities.
Hackers exploit them. They look for the weakest link in the systemand break it.
As soon as a vulnerability is discovered, it’s patched. The updates
you install for your apps or operational system are often just that —patches for newly discovered vulnerabilities.
(Of course, some vulnerabilities can never be patched. Humans,
not machines, are often the weakest link when it comes tocybersecurity. See: social engineering.)
A zero-day vulnerability is unknown to the vendor, and so it hasn't
been patched. The name refers to the number of days a vendor
had to fix the vulnerability — zero. An attack based on thisvulnerability is called a zero-day exploit or zero-day attack.
So even if you keep your system secured, patched, and updated, azero-day exploit may compromise it through a previously unknown
vulnerability. The solution is constant vigilance. Be smart when
online, use strong passwords, don’t click on links if you’re not surethey’re safe.
This way, you’ll minimize your risks and force cybercriminals tolook for easier targets.
Related terms: zero-day vulnerability, zero-day attack.
24