In short, a DoS attack - or Denial-of-Service attack - is a method used to disrupt an authorized user from accessing a target network or site resources. Typically, it is launched by overloading the target (often a site server) with a large amount of traffic, or by sending requests with malicious intent that can cause the target's resources to malfunction or be completely destroyed.

The first recorded case of denial of service occurred in February 2000 where a 15 year old Canadian teenager targeted Amazon and eBay web servers with such an attack. Since then, more and more people have used DoS attacks to disrupt targets in many industries.


Types of DoS attacks

Some types of denial of service attacks aim to disrupt access for a specific target to a network or resource, whereas others aim to make that resource completely unusable. These attacks can last from minutes to hours, and in rare cases, days. The consequences of this type of attack often result in large financial losses for businesses that are targeted and that do not yet have a deterrence strategy in place.

Denial of service attacks can come in many shapes and sizes. Because not all devices and networks are vulnerable in the same way; those trying to have malicious intent will have to get creative with how they exploit the myriad holes in the system configuration.


Some well-known types of denial of service include:

Buffer overflow attack

This is the most common type of attack, a buffer overflow attack relies on sending more traffic to the target than the developer who created the system. This type of attack allows malicious actors to destroy or control the target's processing system.


ICMP Flood

An ICMP flooding attack targets misconfigured devices on a network, forcing them to distribute fake packets to every node (computer) on the target network, rather than just one node, thereby flooding the network. This kind of attack can also be called a “ping of death” or “smurf attack”.

 

SYN Flood

A SYN flood sends a request to connect to a site server but never fully authenticates the connection. Then this attack will target all open ports on the site's server and force them until the server is destroyed.


DoS vs DDoS attacks

A very similar terminology that you may have heard of is a DDoS attack (distributed denial of service attack). The difference between the two is that during a DDoS attack, many malicious machines are aimed at a target resource. A distributed denial-of-service attack is more easily successful in disrupting a target compared to a DoS attack originating only from a single source. Malicious people also tend to use this method because it is very difficult to trace the source of this attack, because these attacks come from many locations.


Can DDoS Attacks Affect Digital Currencies?

In the majority of applications, denial of service attacks have been used to target web servers for large companies, such as banks, online retail companies, as well as government agencies and public services - but it is important to consider that any device, server, or network connected to the internet can be a potential target for this type of attack.

With digital currencies gaining popularity in recent years, cryptocurrency exchanges have become a popular target for DDoS attacks. For example: when Bitcoin Gold was officially released, it was immediately targeted by a major DDoS attack that disrupted their site for several hours.

However, the decentralized aspect of blockchain creates a strong defense against DDoS attacks and other cyber attacks. Even if some nodes fail to communicate or go offline, the blockchain will still operate and validate transactions. By the time the affected nodes can return to normal and return to work, they will resynchronize and download the latest data from the blockchain, which will be provided to the nodes that were not affected by the attack.

The level of protection for each blockchain against these attacks depends on the number of nodes and the hash ratio of the network. The older and bigger a currency is, and Bitcoin is considered the most secure and robust blockchain. This means that DDoS and other cyber attacks will be able to succeed.

The Proof of Work consensus algorithm ensures that network data is secured by cryptographic proof. This means that it is almost impossible to change a block that has already been validated. Changing the Bitcoin blockchain requires a complete, history-by-history dismantling, something that is impossible for even the most powerful computers.

Therefore, a successful attack would probably only be able to modify transactions within the last few blocks and only for a very short time. And if an attacker manages to control more than 50% of Bitcoin's hash power to carry out a 51% attack (or majority attack), the underlying protocol will quickly confirm this as a response to the attack.