Distributed denial of service (DDoS) attacks are a favorite method for attackers to disrupt or debilitate firewalls, online services, and websites by overwhelming systems with malicious traffic or transaction requests. DDoS attackers accomplish this by coordinating an army of compromised machines, or 'bots', into a network of devices they control from a remote location that focuses a stream of activity toward a single target. These botnets may be used to perpetrate DDoS with a range of malicious techniques, including: 

• Saturating bandwidth with massive volumes of traffic,
• Filling up system resources with half-open connection requests
• Crashing web application servers with voluminous requests for random information

The trend is towards shorter attack duration but more immense packet-per-second attack volume. Motives today can include an interest in obtaining a financial reward, making an ideological statement, creating a geopolitical advantage, or exacting revenge for particular government action, corporate campaign, or policy stance.  Types of DDoS attacks can include volumetric, protocol-based, and application-based. DDoS attacks are getting more powerful because they're getting more complex, using many different devices, and targeting other parts of the victim's network. Indeed, attackers are learning that the most basic DDoS attacks are becoming less effective, so they are dropping them in favor of more powerful campaigns.