Types of cyber threat in 2021

To implement and maintain an appropriate level of cyber security, you need to understand the cyber threats your organisation faces.

If terms such as ‘spear phishing’, ‘XSS/cross-site scripting’, ‘DDoS/distributed denial of service’ and ‘SQL injection’ leave you confused, read on.

This page provides a beginner’s guide to the most common types of cyber security threat, the cyber attacks used to deliver them, and the vulnerabilities they attempt to exploit.

Learn more about the scale and nature of cyber crime

Alternatively, if you would like simple explanations, and examples and advice on the common cyber threats to home users, mobile users and consumers, read our bestselling guide Security in the Digital World.

Common cyber threats


Backdoors allow remote access to computers or systems without users’ knowledge.


Formjacking is the process of inserting malicious JavaScript code into online payment forms to harvest customers’ card details.


Cryptojacking is the malicious installation of cryptocurrency mining – or ‘cryptomining’ – software. This software illicitly harnesses the victim’s processing power to mine for cryptocurrency.

DDoS attacks

DDoS (distributed denial-of-service) attacks attempt to disrupt normal web traffic and take targeted websites offline by flooding systems, servers or networks with more requests than they can handle, causing them to crash.

DNS poisoning attacks

DNS (domain name system) poisoning attacks compromise DNS to redirect traffic to malicious sites. Affected sites are not ‘hacked’ themselves.


Malware is a broad term used to describe any file or program intended to harm or disrupt a computer. This includes:

  • Botnet software

    Botnet software is designed to infect large numbers of Internet-connected devices. Some botnets comprise millions of compromised machines, each using a relatively small amount of processing power. This means it can be difficult to detect this type of malware, even when the botnet is running.

  • Ransomware attack

    Ransomware is a form of malware that encrypts victims’ information and demands payment in return for the decryption key. Paying a ransom does not necessarily guarantee that you will be able to recover the encrypted data.  Learn more about ransomware

  • RATs

    RATs (remote-access Trojans) are malware that installs backdoors on targeted systems to give remote access and/or administrative control to malicious users.

  • Rootkits and bootkits

    Rootkits comprise several malicious payloads, such as keyloggers, RATs and viruses, allowing attackers remote access to targeted machines.

    Bootkits are a type of rootkit that can infect start-up code – the software that loads before the operating system.

  • Spyware

    Spyware is a form of malware used to illicitly monitor a user’s computer activity and harvest personal information.

  • Trojan

    A Trojan is a type of malware that disguises itself as legitimate software but performs malicious activity when executed.

  • Viruses and worms

    A computer virus is a piece of malicious code that is installed without the user’s knowledge. Viruses can replicate and spread to other computers by attaching themselves to other computer files.

    Worms are like viruses in that they are self-replicating. However, they do not need to attach themselves to another program to do so.

Common cyber attacks

Cyber criminals deliver malware and other threats via cyber attacks. They might use the following:


Botnets are large networks of compromised computers, whose processing power is used without the user’s knowledge to carry out criminal activity. This can include distributing spam or phishing emails or carrying out DDoS attacks.

Drive-by downloads

Drive-by downloads install malware when victims visit a compromised or malicious website. They don’t rely on unsuspecting users taking action, such as clicking malicious email attachments or links, to infect them.

Exploits and exploit kits

An exploit is a piece of malicious code that can compromise a security vulnerability. Many have been developed by the security services. For instance, in 2017 the WannaCry ransomware spread using an exploit known as EternalBlue. This exploit had been created by and stolen from the US National Security Agency.

Exploit kits are collections of multiple exploits. Available for rent on the dark web, they enable unskilled criminals to automate attacks on known vulnerabilities.

MITM attacks

A MITM (man-in-the-middle) attack occurs when a criminal hacker inserts themselves between a device and a server to intercept communications that can then be read and/or altered.

MITM attacks often happen when a user logs on to an insecure public Wi-Fi network. Attackers can insert themselves between a visitor’s device and the network. The user will then unknowingly pass information through the attacker.

Phishing attacks

Phishing is a method of social engineering used to trick people into divulging sensitive or confidential information, often via email. Not always easy to distinguish from genuine messages, these scams can inflict enormous damage on organisations.

Learn more about phishing

Social engineering

Social engineering is used to deceive and manipulate victims to obtain information or gain access to their computer.

This is achieved by tricking users into clicking malicious links or by physically gaining access to a computer through deception.

SQL injection

A SQL (Structured Query Language) injection occurs when an attacker inserts malicious code into a server that uses SQL. SQL injections are only successful when a security vulnerability exists in an application’s software. Successful SQL attacks will force a server to provide access to or modify data.


Vulnerabilities are the security flaws in your systems that cyber attacks exploit.

The top vulnerabilities are readily available online for the benefit of security professionals and criminal hackers alike.

All a criminal needs to be able to exploit them is a malware toolkit and an online tutorial. There is no need for any coding knowledge whatsoever.

Targeted attacks are more labour-intensive, but, again, rely on tools that are designed to exploit vulnerabilities.

Types of cyber security vulnerability include the following:

  • Network vulnerabilities result from insecure operating systems and network architecture. This includes flaws in servers and hosts, misconfigured wireless network access points and firewalls, and insecure network protocols.
  • Hardware vulnerabilities are exploitable weaknesses in computer hardware. Examples include the Spectre and Meltdown vulnerabilities found in processors manufactured by Intel, ARM and AMD. They affected almost every system, including desktops, laptops, servers and smartphones.
  • Software and application vulnerabilities include coding errors or software responding to certain requests in unintended ways. They include CSRF (cross-site request forgery) and XSS (cross-site scripting) vulnerabilities.
  • Zero-day vulnerabilities are security flaws that have been discovered by criminals but are unknown to, and therefore unpatched by, the software vendors. The term refers to the number of days the vendor has to address the vulnerability. (Zero-day exploits are code that compromise zero-day vulnerabilities.)

Read more about patch management

Cyber attacks

Free infographic: What are the major types of cyber attack?

Download our free infographic to for a handy guide to the major types of cyber attack you might encounter. 

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