Denial-of-Service AttacksDoS Attacks Can Block Your Customers From Doing Business With You

March 22, 2023 | 13 min read

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Denial-of-Service Attacks DoS Attacks

In a Nutshell

A denial-of-service (DoS) attack is where a hacker uses fake data requests to overwhelm your server’s ability to answer connection requests. In other words, they clog up your website with so many fake visitors that your real customers can’t get in. In this post, we explain how they work, why they’re so effective, and what you can do to protect your bottom line.

DoS Attacks: What Does “Denial-of-Service” Mean? How Do You Protect Your Organization?

Online shopping. Googling. Social media. Streaming movies and music. Working from home. The internet has become an integral part of our lives, but we sometimes overlook how much we rely on it.

And, as a result, how easily the balance of our lives can be disrupted.

A denial-of-service attack, or “DoS attack,” is a fairly primitive hacker trick. It relies on fake data requests to overwhelm a server and block access to legitimate users.

These assaults are nothing new. But, they’re growing in popularity as an easy and effective attack method, and have impacted many major companies in recent years. So how does a DoS attack work? Why are they so dangerous, and what can businesses do to protect their revenue?

What is a Denial-of-Service Attack?

Denial of Service Attack

[noun]/də • nī • əl • ov • sər • vəs/

A Denial of Service attack (or “DoS attack”) is an interruption in an authorized user's access to a computer network. This is often done maliciously by attackers who overload network servers through automated activity.

In simple terms, a DoS attack is an attempt to shut down a site or server by overloading it with fake users or false information. Although it’s often labeled as “hacking,” that’s not really correct. Instead of gaining access to a target’s systems, the idea is to block real users from accessing a specific online resource, such as an email account. 

They work because there’s a limit to how much CPU traffic a single system can handle. The DoS perpetrator uses automated programs to flood the targeted server with bogus requests for connection. Successful attacks will either crash the server or slow down access to the point at which legitimate users give up trying to access the site.

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DoS tactics have been around for a long time. They’ve been used for many purposes, including both trolling and online activism. But, they can also be a tool for fraudsters, as we’ll see below.

While denial-of-service attacks had fallen out of the headlines for a while, the technique has recently seen a resurgence. One recent report estimates that DOS attacks are expected to increase by over 300% in 2023.

Did You Know?

A simple denial-of-service attempt can be launched from a single computer. In contrast, an organized attack that comes from multiple sources is referred to as a distributed denial-of-service, or DDoS.

Why Do DoS Attacks Happen?

Like we referenced above, the reasons for denial-of-service assaults are varied.

Professional attacks may be an attempt to disrupt a competitor’s organization. Or, it may be to protest a social issue, or draw attention to a political cause. They could even be launched out of spite, or as a means of revenge.

In an earlier era of the internet, people commonly set DoS attacks in motion just to prove they could. Recently, we’ve seen more instances in which attacks are motivated by:

Denial-of-Service Attacks


Governments or opposition political parties sometimes use DoS attacks against their enemies.  We’ve seen this activity surge  since the beginning of the War in Ukraine in particular. Both sides are using DoS attacks to either shut down important websites or block access to crucial servers, hoping to interfere with their opponent’s operations.

Denial-of-Service Attacks

Monetary Gain

Extortion is also a common reason behind DoS attacks. Attackers can freeze up a website with fake traffic and blackmail the owner, who must pay to have the site released. Experts worry that this type of attack could be used against hospitals, power grids, or other critical services, where paying the ransom may literally be a matter of life or death.

Denial-of-Service Attacks


Finally, it’s not uncommon for hackers to use a DoS attack as a distraction for a different, larger operation, such as a security breach. The assault keeps the target’s IT department so focused that the more dangerous crime is not discovered until it’s too late.

How Do Denial-of-Service Attacks Work?

As with most malicious online attacks, there are a variety of techniques for accomplishing the same goal. Most fall back on one of three tactics:

Flooding Attacks

An attacker saturates the targeted system with more HTTP requests than that system can handle. This leads to a flood of incomplete connections that eat up operating resources. The server becomes overwhelmed, slowing down or denying access to actual users.

Note that to be effective, a flooding attack requires the attacker to have more available bandwidth than the target. This is why many DoS attacks are distributed across multiple users (a distributed-denial-of-service, or “DDoS” attack).

Buffer Overflow Attacks

A buffer overflow attack doesn’t rely on a flood of individual connection requests. Rather, the attacker attempts to feed bigger information packets than a machine’s memory buffers can handle.

Once the server has maxed out all available disk space and memory, it can only create more space by overwriting portions of the buffer. Since those earlier connections have not yet been resolved, the memory stack becomes corrupted, leading to slower processing or a total crash.

Unintentional Cases

Sometimes, a DoS event turns out to be a natural occurrence. A recent example is the website for Ticketmaster, a US-based ticket sales and distribution company. Fans trying to secure tickets for the final days of Eurovision were frustrated when sessions timed out due to the slowness of the server before the entire system went down.

Symptoms of a DoS Attack

Remember: denial of service can happen for very legitimate reasons. An overloaded server or a system with maxed-out memory do not necessarily indicate malicious activity.

It can be tricky to identify a malicious assault. That makes it important to recognize some of the most common red flags of an attack, including:

  • Inability to access a particular network or website
  • Unusually slow or irregular network performance
  • 503 “Service Unavailable” errors
  • Unexplainable spikes in network traffic
  • A large number of requests from the same IP address in a short period of time

For the best chance of detecting an attack, you really have to establish a benchmark for typical network activity over a given period of time. Knowing what’s “normal” for a given site enables you to distinguish possible DoS attacks in their early stages. 

When creating your baseline, be sure to factor in periods where an increase in traffic volume is to be expected. For instance, if you’re running an eCommerce business, you should expect a surge in activity during the holiday season. Then, once a normal traffic pattern has been established, it will need to be monitored on an ongoing basis.

Impact of DoS Attacks

Dealing with denial-of-service attacks can be a serious hassle. Your site may be inaccessible for hours, even days, depending on the scale of the attack. That said, there are also some negative impacts to be aware of even beyond the scope of the attack itself, including:

Ransom Costs

The reason behind a DoS attack becomes immediately apparent if followed by a demand for payment. The attackers demand an exorbitant ransom payment, usually in cryptocurrency, before they’ll release the server. Of course, there’s no guarantee that the attack will stop, or that they won’t try again later, knowing that you’ll pay the ransom.

Other Financial Losses

Depending on the type of business, the costs of downtime can be staggering. A one-hour outage cost Amazon an estimated $34 million in sales in 2021, while a 20-minute crash that same year cost billions for Chinese eCommerce market Alibaba. For smaller organizations that don’t have as much leeway, having systems go down at all can be disastrous.

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Lost Productivity

In the age of Zoom meetings and subscription software, inaccessible servers can be devastating to productivity. At the same time, IT departments and customer relations teams will be pulled from their normal activities as all resources are allocated to getting systems functional. This means hold ups and delays for other essential functions.

Brand Damage

Consumers need to feel you’ll be consistently online and available. Even one denial of service event could cause a customer to take their business elsewhere. Even worse, they may turn to review sites or social media channels to proclaim your lack of dependability.

Customer Disputes

One of the leading causes of customer disputes is poor service. A denial-of-service attack can make it difficult (or impossible) to resolve customer inquiries quickly and efficiently. Frustrated shoppers may decide it’s easier to call the bank and file a chargeback. If you’re a merchant, this will create even more financial stress for you than the initial attack.

How to Prevent DoS Attacks

There’s no sure-fire way to stop every denial-of-service attack. However, there are steps you can take to help mitigate risk.

DoS attack prevention can be broken down into four key actions:

Use all Available Tools

Make sure your system administrators are deploying every type of DoS prevention at their disposal. There is no silver bullet here: you’ll likely need multiple tools and techniques to maximize protection. Check that your providers have preventative measures in place as well, and can balance loads across multiple servers if needed.

Maintain Malware Protection

While DoS attacks are designed to block access, some attackers take advantage of buffer overload and use the opportunity to install viruses and malware. It’s critical for organizations to maintain proven anti-virus and anti-malware solutions.

Monitor Systems

Implement strong firewalls and intrusion prevention systems, then use these tools to monitor traffic. Be sure monitoring systems are set to send alerts when traffic increases inexplicably. This may allow you to block suspicious traffic before serious damage is done.

Stay Up to Date

The best protection comes from using the most current software. Conducting regular updates ensure that you’re protected against new and developing tactics. You’ll want to install those updates as quickly as possible.

Responding to DoS Attacks

It’s impossible to eliminate all denial-of-service threats. That said, having a response plan in place ahead of time can help you limit the impact of an attack and get back up and running quickly.

The most obvious requirement is creating current backups of data and mandatory applications. Backups should be performed consistently and tested on a regular schedule. Be sure staff members are clear on their responsibilities in an emergency situation.

Your plan should also define a specific course of action in the event of a successful attack:

Make Certain it Actually is An Attack

If you’ve taken the time to create a benchmark for normal traffic, you may be able to identify and quantify fluctuations. DoS red flags such as slow processing, system crashes, or erratic network performance could also indicate other problems. Matching traffic against your baseline can alert you to potential attacks, but can also help you see if something is an outlier, or an assault.

Do Damage Control

This is where your recovery plan comes into play. As soon as an attack is detected, limit the damage by sealing off your organization’s network perimeter and securing any exposed assets. Do an immediate check for other malicious activity that may have occuring during the DoS attack. Alert users that there is a temporary issue, and alert service providers to the situation at once.

Get Back to Business

One of the things that should be factored into your recovery plan is a timeline for re-establishing connections. Get the most important systems up and running first, then communicate to customers that services are back online. Once the situation has been resolved, try to identify why the attack was successful, and make appropriate updates to your response plan to prevent future incidents.

DoS Attack Management: A Long-Term Process

DoS attacks were once the go-to technique that cybercriminals and online activists alike relied on to disrupt the normal operation of digital services. As more sophisticated tools became available, interest in DoS attacks seemed to wane. But, they’re becoming popular once again.

These assaults may not directly cause the loss of money or data-related assets. However, they still end up costing organizations significant amounts of time and resources, and may lead to customer disputes and chargebacks.

The most effective method of DoS mitigation is to prevent attacks from happening in the first place.

Up-to-date systems and virus protection tools, employee training, and vigilance are all good methods of combating DoS attacks. Even if an attack is successful, having a response and recovery plan already in place can limit the impact.

In fact, prevention is usually the best way to deal with any type of computer-based crime, including fraud and account takeover attempts. A comprehensive strategy can help identify threats before they happen, and protect your business and revenue. To learn how we can help, speak to one of our experts today.


What does a denial of service attack do?

DoS attacks are designed to slow or block access to your servers by overwhelming the system with too many requests, or slowing it down with malicious software.

What is the difference between DoS and DDoS?

Denial-of-service attacks typically come from one person or machine. Distributed-denial-of-service (DDoS) incidents use multiple machines, IP addresses, and systems, making it almost impossible to trace the actual attacker (or attackers).

How long will a DoS attack last?

The duration of a denial-of-service attack will vary by the tactics and techniques used. It’s also in flux right now, as there has been a surge in DoS activity following the war in Ukraine. In Q2 of 2021, the average DoS attack lasted 30 minutes. One year later, the average is more than 48 hours.

Can DoS attacks be stopped?

Simple DoS attacks can often be blocked through vigilance and good overall network security. More sophisticated assaults can be more difficult, though. Keep in mind that your host internet service provider should also have measures in place to prevent or stop DoS attacks.

Why do DoS attacks still work?

The basic reason is that online servers and systems have a limit to how much traffic they can process at one time. As long as attackers have more memory and processing speed, they can typically find a way to commit DoS attacks.

Is a DoS attack a crime?

Yes. According to the FBI and other law enforcement agencies, denial of service attacks fall under the category of cybercrimes, and perpetrators are routinely jailed for the activity.

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