A Denial of Service (DoS) attack is a malicious attempt to make a website or online service unavailable to its intended users by overwhelming it with a flood of illegitimate traffic. This flood of traffic typically comes from multiple sources, often coordinated by attackers using botnets (networks of compromised computers). The goal is to exhaust the target server’s resources such as bandwidth, processing power, or memory, rendering it unable to respond to legitimate user requests.

DoS attacks can disrupt businesses, cause financial losses, and damage reputation. They may also serve as a distraction while attackers carry out other malicious activities. More sophisticated variants include Distributed Denial of Service (DDoS) attacks, which amplify the volume of malicious traffic by using multiple compromised devices.

Preventing DoS attacks involves several strategies:

1. Network Security: Implementing firewalls and intrusion detection/prevention systems (IDS/IPS) can help filter and block malicious traffic before it reaches the target server.
2. Traffic Management: Using load balancers and content delivery networks (CDNs) can distribute incoming traffic across multiple servers, reducing the impact of a DoS attack on any single server.
3. Rate Limiting: Setting limits on the number of requests a server can accept from a single IP address or source can help mitigate the impact of flood attacks.
4. Monitoring and Response: Regularly monitoring network traffic and server performance can help detect and mitigate DoS attacks early. Having a response plan in place allows for quick action to minimize downtime and restore services.
5. Up-to-date Software: Keeping server software, operating systems, and security patches up to date helps mitigate vulnerabilities that attackers may exploit to launch DoS attacks.

By combining these preventive measures, organizations can significantly reduce the risk of falling victim to DoS attacks and maintain the availability and reliability of their online services.