DDoS stands for Distributed denial-of-service or Denial-of-service attack. DDoS attack is an attempt to make machine or network unavailable to its intended users. The attacker sends or implants malware into a file or emails. When the victim downloads or opens the emails, DDoS attacks the computer hardware and others. Under a DDoS attack, hackers send multiple connections continuously to the server. The attack takes place from multiple IP addresses. It takes up the network bandwidth and uses up system resource.