Copyright Goodheart-Willcox Co., Inc. 272 Principles of Cybersecurity Denial of Service Attacks Denial of service (DoS) attacks are hacks against the availability of data. DoS attacks do not steal or destroy data. Rather, they are intended to prevent right- ful users from accessing systems. Recall the CIA triad. Sadly, DoS attacks happen quite frequently. Some are severe, such as the one described in Chapter 1 that tar- geted Estonia. If a company has the right preventative plan in place, DoS attacks can be resolved quickly. This was the case in the attack against several bitcoin exchanges in June 2017. One of those companies, Bitfi nex.com, was the largest US provider of bitcoin currencies. It tweeted it was under a DDoS attack, but resumed operations within an hour. The most common DoS attack is a DDoS attack. In a distributed denial of service (DDoS) attack, many hosts are contributing in attacking the victim, as shown in Figure 8-21. Most often, those hosts are under the control of malware. The hosts, then, are known as bots. Bot is a shortened form of robot. Hosts are con- sidered bots when their actions are being controlled by another device. There are two types of denial of service attack: Smurf attack and SYN fl ood. Smurf Attack A Smurf attack involves overwhelming the victim’s computer with ICMP requests. When a target host is pinged, by default, it essentially asks “Hey, are you there?” several times. Each question generates a response from the target host. In a Smurf attack, the victim is overwhelmed attempting to reply to all of the “Are you there?” questions. For this reason, this type of attack is also known as a ping fl ood. CompTIA Security+ 1.2 MTA Security Fundamentals 3.3 Want to see attacks in real time? Check out the Norse website (www.norsecorp.com) and use the Live Attacks link to see a map of attacks as they happen. FYI Attacker (bot) Attacker (bot) Attacker (bot) Attacker (bot) Attacker (bot) Attacker (bot) Victim (server) Goodheart-Willcox Publisher photos: Denis Rozhnovsky/Shutterstock.com Figure 8-21. A distributed denial of service attack involves many hosts, usually infected with malware, attack- ing a single server.