denial of service attack

 Guide to DoS Attacks: Protection and Prevention

A DoS or denial of service attack is used to bind a website’s resources so that users who need to access the site can’t do so. Many large enterprises have been the focus of DoS attacks. Since it can be easily executed from almost any location, finding those responsible can be quite difficult.

Difficult to deal with and potentially costly, DoS attacks can cause blackouts of web sites and network services for organizations, small and large. They can also be profitable for criminals, some of whom leverage these cybersecurity attacks to shake down companies for anywhere from thousands to millions of dollars.

The following lines will explain everything about denial of service attacks, including their history, how they work, and how to stay safe – plus what is DDoS attack.


DoS attacks on Internet-based systems have a long history that began with the Robert Tappan Morris worm attack in 1988. In that venture, Morris, a graduate student at MIT, unleashed a self-reproducing piece of malware – a worm, that rapidly spread through the global Internet and triggered attacks and buffer overflow on the affected systems.

Those connected to the Web at the time were mostly academic and research organizations, but it was estimated that 10% of the 60,000 systems in the USA were affected. Damages were estimated to be as high as $100 million, according to the U.S. General Accounting Office. Robert was successfully prosecuted under the 1986 Computer Fraud and Abuse Act and sentenced to 3 years’ probation, 400 hours of community service and was fined $10,000.

What is a denial-of-service attack?

It’s a form of cyber-attack in which a malicious actor intends to render a computer or other device unavailable to its intended users by interrupting the device’s regular running. These attacks typically function by saturating or overwhelming a targeted device with requests until standard traffic is unable to be processed, bringing in denial-of-service to users. This attack is characterized by utilizing a single computer to perform the attack.

what is a denial of service attack

How Does a DoS Attack Work?

Unlike a malware or virus, a denied of service assault doesn’t rely on a special program to run. Instead, it leverages an inherent vulnerability in the manner computer networks communicate.

Here’s one denial of service attack example. Suppose you visit a Shopify in order to shop for a gift. Your device sends a small package of information to the website. The package runs as a “hello” – basically, your device says, “Hi, I would like to visit you, can you let me in.”

When the server receives your  message, it sends a short one back, saying, in a sense, “OK, are you real?” Your PC responds — “Yes!” — and communication is established.

The site’s homepage then pops up on your screen, and you can explore the website. Your PC and the server continue communicating as place orders, click links, and carry out other activities.

In this attack, a computer is manipulated to send not just one “introduction” to a server, but hundreds or thousands. The server — which can’t show that the introductions are fake — sends back its usual response, waiting to a minute in each request to get a reply. When it gets no answer, the server shuts down the connection, and the machine is executing the attack repeats, sending a new batch of bogus requests.

These attacks mostly affect businesses and how they run in a connected world. For consumers, the attacks obstruct their ability to access information and service.

DoS weapons of choice

The following are some of the “weapons of choice that can be utilized to execute these strikes.

  • Nemesy – It can be utilized to generate random packets. It works on windows. Thanks to the nature of the program, if you have an antivirus, it will most likely be detected as a virus;
  • Land and Altieri – this tool can be used for IP spoofing and opening TCP connections;
  • Panther – This tool can be exploited to flood a target network with UDP packets;
  • Botnets – these are multitudes of compromised computers on the Internet that can be used to perform a distributed denial-of-service attack.


DoS attacks typically fall in seven categories:

  • Buffer overflow attacks – An attack in which a memory buffer overflow can cause a PC to consume all available hard disk space, CPU time, or memory. This type of exploit often results in sluggish behavior, system crashes, or other harmful server behaviors, resulting in DoS;
  • Flood attacks – By flooding a targeted server with an oversaturating amount of packets, a treat actor is able to overwhelm server capacity, resulting in a denial of service. In order for most flood assaults to be successful, the hacker must have more available bandwidth than the target;
  • SYN attack – This form of attack takes advantage of the 3-way handshake to establish communication utilizing TCP. SYN attack works by saturating the victim with incomplete SYN messages. This causes the victim device to allocate memory resources that are never used and deny access to legit users;
denial of service attack example
  • Teardrop – This sort of attack uses large data packages. TCP/IP breaks them into fragments – assembled on the receiving host. The attacker manipulates the packets as they sent so that they overlap each other. It can cause a target to crash as it tries to re-assemble the packages;
  • Smurf – In a Smurf strike, the malicious actor sends ICMP (Internet Control Message Protocol) broadcast packages to a number of hosts with a spoofed source IP address that belongs to the target device. The recipients of these spoofed packages will then respond, and the targeted host will be saturated with those responses;
  • Ping flood – This attack is based on overwhelming a target with ICMP (ping) packages. By inundating a victim with more pings than it’s able to respond to efficiently, denial of service can occur. This assault can also be used as a DDoS attack;
  • Ping of death – Often combined with a ping flood attack, this attack includes sending a malformed package to a targeted device, resulting in deleterious behavior like system crashes.

How Do I Know if I’m a Victim of DoS Attack?

Indicators of a denied-of-service attack can look like non-malicious availability problems, like technical issues with a specific network or a system administrator performing maintenance. Still, the following signals could indicate this attack:

  • Sluggish network performance (accessing websites or opening files);
  • Unavailability of a particular website;
  • An inability to access any site.

The best way to detect and identify this attack is through network traffic monitoring and analysis. Network traffic can be monitored using a firewall or intrusion detection system. An administrator may set up rules that create an alert upon the detection of an atypical traffic load and determine the source of the traffic or drops network packages that satisfy certain criteria.

how to prevent dos attacks

How to Prevent DoS Attacks?

If you depend on a website to do business, then you want to know everything about DoS attack prevention. Rule of the thumb – the earlier you can identify an attack-in-progress, the faster you can contain the damage. Here are a few things you can do.

Get help identifying attacks

Businesses often use technology or anti-DoS services to defend themselves. It can help you recognize between legitimate spikes in network traffic and a denial-of-service attack.

Notify your ISP

If you notice your organization is under attack, you should contact your Internet Service Provider as soon as possible to identify if your traffic can be rerouted. Having a backup ISP is a great idea, too. Also, consider services that can diverge the big DoS traffic among a network of servers. This can help render an attack ineffective.

Black hole routing

Internet service providers can utilize black hole routing. It leads to excessive traffic into a null route, sometimes called a black hole. It can help prevent the targeted network or website from crashing. The downside is that both illegitimate and legitimate traffic is rerouted in the same route.

Configure routers and firewalls

Routers and firewalls should be configured to reject fake traffic. Remember to keep your firewalls and routers updated with the latest security patches.

Use front-end hardware

App front-end hardware that’s incorporated into the network before traffic reaches a server can analyze and screen data packages. The hardware classifies the data as a priority, regular, or dangerous as they enter a system. It can also block threatening data.

How Does an Attacker Release It?

There are various ways that an attacker can launch this type of cyber attack. They span from simply unplugging a server from the network (physical access) to coordinating large armies of zombie devices to launch a large scale distributed strike against their target utilizing:

  • Buffer overflows in the app functions;
  • Malformed data to increase unexpected exceptions;
  • Exploited race conditions in multi-threaded platforms;
  • Heavy-duty SQL queries by web forms and “spamming” them with requests, (inserting % characters within search query fields);
  • SQL injection assaults performing recursive CPU-intensive queries;
  • The end-users’ web browsers to overload the app with parallel requests through persistent/ reflected cross-site scripting attacks;
  • Overly-complex regular expressions within search queries;
  • Super large files uploaded to the server.

What is DDoS?

A DDoS or distributed denial-of-service attack is a harmful attempt to obstruct normal traffic of a targeted network, server, or service by overwhelming the target or its surrounding infrastructure with a flood of traffic.
Distributed denial of service attacks accomplish effectiveness by using multiple compromised computer systems as sources of attack traffic.

Exploited devices can include computers and other networked resources like IoT devices. For example, a DDoS attack is like a traffic jam clogging up the highway, preventing your vehicle from getting at its desired destination.

How DDoS Attack Works?

It’ll attempt to make a website or online service unavailable by flooding it with undesired traffic from multiple devices. The culprit can then instruct and control the botnet, commanding it to flood a certain website with traffic – so much that its network stops working, taking the website offline.

what happens during a ddos attack

What Happens During a DDoS attack?

During distributed denial of service attacks, there is an attempt to stop legitimate visitors from accessing the data normally available on the site, access private data, vandalize a website, or completely shut down a server or service. It can happen to businesses and sites in any industry – from financial services like banks to B2B or e-commerce.

Throughout the attack, hackers may flood a network with information and requests. Flooding can be achieved by a dedicated group of attackers voluntarily using their own devices – such as from a hacktivist group or other organized crew – or they can hijack computers to use for the assault. Attackers may also scan servers and apps for potential exploits or try to access sensitive data.

DoS Attack vs. DDoS attack

The main difference between DoS and DDoS is the number of connections used in the attack. Some denial of service attacks, such as “low and slow” attacks like R.Y.D.Y. derive their power in the simplicity and minimal requirements required to them be productive.

Denial of service attack applies a single connection, while a DDoS attack uses many sources of attack traffic, often in the botnet model. Generally, many of the attacks are fundamentally similar and can be executed, utilizing many sources of malicious traffic.


Organizations are increasingly alert to the fact that security attacks are a bigger financial threat to performance degradation than on the outage. While outages cost more per minute, slowdowns take up 10 times more time and can ultimately cost more. Staying careful and implementing the above-mentioned security practices can prevent your business from falling victim to a DoS attack.

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