What Is Denial Of Service (DOS)?

Denial of service or DoS attacks is used to completely shut down a network or machine, making it inaccessible for its users.

A DoS attack is usually made by diverting loads of traffic/information to cause a crash. This is known as flooding and can restrict account holders, members, employees, etc., from using the dedicated resource or service.

Targeted users or servers often belong to high-profile companies like banks, media, and those in the commercial sector. Even though the intent is not to steal user data or other assets, the inflicted company often has to spend loads of money and resources to fix the situation.

How Does A DoS Attack Work?

With increased digital communication and transactions, DoS attacks have become more common.

Cyberattackers launch a denial of service attack to steal PII (personally identifiable information), damaging a company’s reputation and burdening them financially.

A data breach or attack may target one company at a time or attack several hosts belonging to different organizations. Often, companies with higher-end security are attacked by members of their supply chain.

Multiple company attacks call for a DoS attack approach triggered through one internet connection. Using a single device and multiple requests to the target server causes a bandwidth overload.

  • Any CPU or RAM vulnerabilities are used in the attacks.
  • A firewall with accept/deny rules can repair the damage done by a DoS attack.
  • Restricting malicious IP addresses can prevent a DoS attack as any cyber attack uses one IP to cause an overload.
  • DDoS attacks or distributed denial-of-service are more powerful and far less easy to detect.

What Is A DDoS Attack?

The DDoS attack or distributed denial of service DoS is a type of DoS attack in which the attacker floods the target with abnormal internet traffic. This prevents regular traffic from reaching its intended destination.

Smartphones, IoT devices, PCs, networks reverse, etc., channel extra traffic to the targeted company’s website, mobile app, software programs, and data infrastructure.

DDoS and DoS attacks slow down a server and cause multiple services to halt. These include websites, apps, online resources, and email systems.

Different sources used to attack a system often operate in the form of a botnet. A botnet is a network made by the connection of personal devices that cyber attackers have compromised without the consent or knowledge of its users.

Attackers use malicious software to attack multiple systems, so spam and fake requests can be directed toward PCs and other devices. A targeted system will experience an overload of attack traffic due to tens of thousands of fake network resource requests.

Most company servers are attached to multiple sources, so identifying exactly who the attacker is, becomes quite difficult. Differentiating between regular and spammy traffic is also nearly impossible, which is why DDoS attacks prove harmful.

Why Are DDoS Attacks Created?

DDoS attacks or distributed denial of service attacks are not initiated to steal information; they are made to prevent attached legitimate users from accessing a server or network.

Some DDoS attacks may be a facade for other malicious intents. This includes destroying a site’s firewall system or weakening the security code to set a base for future attacks.

DDoS attacks also work as digital supply chain attacks. Cybercriminals attack one weak target link if they cannot penetrate the security system of several connected websites. This allows the initial target to get compromised easily.

New ways to attack are always budding. Any device with internet access and poor security protocols is prone to an attack.

What Do Cyber Attackers Achieve From A DDoS Attack?

There are several reasons why cybercriminals use a DDoS attack. Some of these include:

  • Stealing financial information.
  • Breaching sensitive or personal data.
  • Obtaining PII.
  • Attacking government departments and agencies gives them a bad reputation.
  • Grabbing email ID and login credentials.
  • Leaking trading secrets, product designs, and other intellectual company assets/property.
  • Accessing IT infrastructure.

DoS Attack History

The Robert Morris worm attack in 1988, designed by an MIT (Massachusetts Institute of Technology) student with the same name, was the first denial of service attack on internet-connected systems.

Morris released a self-reproducing worm or malware that used the internet to spread crazily and slow down buffering on inflicted systems.

People using the internet at the time included those with academic or research backgrounds. Nearly 10 percent out of 60k systems across the United States were affected.

Damages amounted to 10 million dollars as reported by GAO (General Accounting Office). Morris was prosecuted under the CFAA (Computer Fraud and Abuse Act 1986) and was sentenced to a 3-year probationary period, four hundred hours of community service with a 10k dollar fine.

DoS/DDoS Attacks Throughout History

  • Imperva, a network security company, was attacked on 30th April 2019. A huge denial of service DoS attack was tracked against one of the company’s clients. The attack was launched at 580 million packets/second but was nullified due to DDoS protection software.
  • GitHub.com became unavailable on 28th February 2018 due to a DDoS attack. The website went offline in under ten minutes. Thousands of endpoints were attacked (1.35 terabits/second and 126.9 million packets/second).
  • Dyn hosting provides domain hosting to popular websites and companies. In 2016, it was attacked by massive traffic, which caused popular connected sites like Twitter, Amazon, PayPal, Spotify, Airbnb, and Netflix to go down. Mirai, a botnet, was used to trigger 500k devices to divert immense traffic. This botnet could access IoT devices that were used to dismantle the server.
  • AWS (Amazon Web Services) mentioned in its AWS Shield Threat Landscape Report Q1 of 2020 that it faced a huge DDoS attack in February of 220. The volume was 2-3 terabytes/second and was 44 percent larger than in previous attacks. The attackers used CLDAP (Connection-less Lightweight Directory Access Protocol), a type of UDP vector countered using the AWS Shield.

What Are The Different Kinds Of DoS Attacks?

DoS attacks and DDoS can be launched using different kinds of methods. Common types include:

Buffer Overflow

This attacking method sends traffic beyond a network’s set limits.

Application Layer

Such an attack uses fake traffic to bring down application servers like DNS (domain name system) and HTTP (Hypertext Transfer Protocol).

The application layer attacks security vulnerabilities to send massive network traffic to an application’s protocol or server.

Ping Of Death

The ping protocol is abused in this attack by oversized requests using payloads. This causes the target system to be burdened, forcing it to stop responding to actual requests and causing crashes.

DNS Amplification

A DNS denial of service attack creates requests that look like actual requests from the IP address. These are then sent to misconfigured DNS servers that third parties often manage. As soon as the DNS responds to these fake requests, amplification occurs.

Added information from intermediate DNS servers is greater than regular, requiring extra processing. The load may ultimately cause users to be denied access to the service.

State Exhaustion

State exhaustion is also called TCP (Transmission Control Protocol). An attacker fills state tables in routers, network devices, and firewalls with attack code.

When stateful inspection happens, these devices fill state tables by opening excess TCP circuits, causing a network crash.


This is a type of denial of service attack that uses network bandwidth to target resources. A huge amount of legitimate traffic is diverted to the target’s system, causing a flood using UDP or ICMP (Internet Control Message Protocol).

Network devices face an overload due to the inability to detect malicious code and extra network packets.

SYN Flood

Such an attack plays with the TCP handshake protocol to cause a higher volume of request streams to open added TCP connections. Flood attacks cause these circuits to be left incomplete and deny users access to the server.


Teardrop detects flaws in older OS by attacking fragmented IP packets. Large packets cannot be handled by intermediary routers and require fragment offsets.

Hosts face a system crash due to the OS failing to reassemble the fragments.

What Are The Signs Of A DoS Attack?

  • Inability to access files and websites on a network.
  • Spam email.
  • Slow network performance.

How To Prevent A DoS Attack?

  • Slow network or internet speed should always be verified with an ISP or cloud service provider to determine the underlying cause.
  • Alerting your ISP allows them to divert malicious traffic away from your network. They can also reduce the security of such an attack by using lead balancers.
  • An ISP may also use IDSes (intrusion detection systems), firewalls, cloud-based anti-DoS, and backup ISP to ensure the safety of network resources.

Final Thoughts

DDoS and DoS attacks (denial of service) may be quite damaging. They can easily ruin a company’s reputation and cause a financial burden by forcing it to spend on repairs.

Using protective software and firewalls, only allowing access to trusted third parties, and working with your ISP can help you reduce the severity or prevent denial of service DoS.

Derik Belair

As President and CEO, Derik leads the vision, strategy and growth of Augmentt. Prior to founding Augmentt, Derik was the Vice President at SolarWinds, leading the digital marketing strategy for SolarWinds’ Cloud division. Derik has been working in the channel for over 20 years, starting his career as a channel sales rep at Corel Corp. and eventually becoming the first employee at N-able Technologies in April of 2000.
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