A Denial of Service (DoS) attack is a type of digital attack on a system or individual which attempts to remove the victim from a network and make them unavailable to their peers. DoS attacks typically spam the victim and exhaust their resources, preventing them from servicing legitimate requests from peers or clients. A Distributed Denial of Service (DDoS) attack is a common type of DoS attack which uses a distributed group of attacking computers to target one or several targets.

DDoS attacks are often more difficult to prevent because the attack comes from many sources, so blocking a single source does not stop the attack. In open, peer-to-peer networks such as Bitcoin, DoS attacks must be carefully guarded against, as there are often fewer methods for eliminating malicious actors from the network. Preventing DoS attacks is the main reason Script, Bitcoin’s scripting language, is not Turing complete.

If validating a Bitcoin transaction could use loops, it could potentially use an infinite loop, which would prevent Bitcoin nodes from validating additional transactions and blocks. This would eventually take nodes offline and crash the network. Denial of Service attacks can be combined with eclipse attacks in order to cut a victim off from the broader network and then flood them with dishonest information in an attempt to convince the victim that they are receiving the dishonest information from the broader network.

Denial of Service attacks can also be paired with phishing attacks. If an attacker can execute a DoS attack on a website, they may be able to put up their own malicious version of the same website and convince users to use the malicious version. Users of the website may then be tricked into inputting sensitive information such as passwords or credit card numbers.

!Key Fact: You can reduce the chances of falling for a phishing attack by always double-checking the URL and HTTPS security of sites you use for financial transactions or personal identification. You can reduce the chances of falling for a phishing attack by always double-checking the URL and HTTPS security of sites you use for financial transactions or personal identification.