What is DDoS? How to recognize and prevent DDoS attacks effectively

In the digital age, cyber attacks are becoming more sophisticated and complex. One of the most common forms of attack that causes serious damage to businesses and website systems is DDoS attacks. So What is DDoS?? Why is this form of attack dangerous? How to effectively prevent DDoS in 2025? In this article, Antidetect Browser Hidemium will help you understand the nature of DDoS, how to recognize the signs of an attack, and the technical solutions and security strategies needed to protect your systems against this ever-evolving threat.

1. What is DDoS?

DDoS (Distributed Denial of Service) is a form of distributed denial of service cyber attack. In it, an attacker uses a large network of controlled computers (called a botnet) to send a large number of requests to a specific server, website or service, in order to overload the system so that it cannot handle legitimate traffic from real users.

DDoS is different from DoS (Denial of Service) in that DoS only uses one attack source, while DDoS is an attack from many sources, so the level of danger and handling ability are also much more complicated.

DDoS is a form of denial of service attack that overloads servers and computer networks.

2. Common forms of DDoS attacks today

When you learn about what a DDoS attack is, you will see that there are many different forms that hackers use to cause disruption and damage to systems. Each type of DDoS attack has its own operating mechanism and goals, from blocking bandwidth, exploiting carrier protocol weaknesses to tricking applications into causing serious problems. Here are some common forms of DDoS attacks that organizations should be aware of:

2.1 SYN Flood

SYN Flood is one of the most common forms of DDoS attack, exploiting a weakness in the TCP three-way handshake. The goal of this attack is to consume server resources by creating a flood of connections that makes the system unable to handle legitimate connections from real users.

In a SYN Flood attack, hackers send SYN packets from spoofed IP addresses to the target server. When the server responds with a SYN - ACK packet, it waits for a final response (ACK) to complete the connection. However, this response never arrives, causing the server to remain in a “waiting” state for a certain amount of time. As the number of connections increases, the server becomes overloaded and cannot accept any more valid requests.

SYN Flood is a common type of DDoS attack.

2.2 UDP Flood 

In a UDP Flood attack, a hacker sends a large number of UDP packets to a random number of ports on the target server. For each packet, the server checks to see if there is an application listening on the specified port. If no matching application is found, the server automatically resends a packet. ICMP Destination Unreachableto announce that “there is no service at this port”.

Having to process and respond to such a large number of requests quickly consumes system resources: from CPU, RAM to network bandwidth. If the attack lasts long enough and the data sent is large enough, the server may become overloaded and unable to serve legitimate user access.

Suppose a DNS server is running normally. When attacked by a UDP Flood, the system will continuously receive invalid UDP packets to random ports. The DNS server is then distributed resources to process meaningless queries, slowing down or stopping the user's valid domain name lookup.

>>>Learn more: What is DNS 1.1.1.1? Easy guide to install & change DNS 1.1.1.1

2.3 HTTP Flood 

HTTP Flood is one of the most common and difficult to detect application layer (layer 7) DDoS attacks today. Unlike network layer attacks that use large traffic to overload bandwidth, HTTP Flood uses valid requests via HTTP or HTTPS protocol to be forced to process and overload.

An attacker sends a large number of HTTP GET or POST requests to a website, API, or web application, with the intention of causing the server to continuously process and consume resources such as CPU, RAM, and database connections. Because these requests look like real users, it is difficult for a normal firewall or load balancing system to distinguish them.

For example, an e-commerce website has a product search feature. A hacker can send thousands of random search queries at high frequency, forcing the backend server to continuously process database queries. Without access limits or filters, the website will slow down or crash completely.

✅ Effective ways to prevent HTTP Flood:

• Install Web Application Firewall (WAF) to filter malicious HTTP requests.
• Use CAPTCHA for user authentication for actions that are susceptible to abuse.
• Rate Limiting Based on IP, session or User-Agent.
• Integrate advanced anti-DDoS solutions, such as Cloudflare, Akamai Bot Manager, or an anonymous proxy from Hidemium to hide and protect the origin server.

2.4 Ping of Death

Ping of Death (POD) is a classic form of DDoS attack that exploits a vulnerability in the operating system's ICMP packet handling. Although less common than HTTP Floods, Ping of Death can still cause serious consequences if the system is not updated or has weak security configurations.

When performing a POD attack, the hacker will send Ping packets that are corrupted or have an excessive size (over 65,535 bytes – the maximum in the IP standard). These large packets will be broken down during transmission. When the target server tries to reassemble them for processing, the total size exceeds the buffer capacity, leading to a memory overflow error, causing the system to freeze, reboot, or crash.

Ping of Death (POD) is a form of DDoS attack that causes systems to become unstable, freeze, or stop working.

2.5 Smurf Attack

Smurf Attack is a form of DDoS amplification attack (amplification attack), exploiting weaknesses in IP and ICMP protocols to flood the victim's bandwidth. Although similar to Ping Flood, Smurf Attack is more dangerous because it uses fake network IP addresses and utilizes intermediate networks to expand the attack scale.

The attacker sends malicious ICMP packets with spoofed IP addresses to the broadcast network, causing servers on the network to send a series of responses to the victim's IP address. As more servers respond, the target IP address is flooded with traffic, causing the device to become inoperable because it cannot handle any more requests.

2.6 Fraggle Attack

Fraggle Attack is a variation of Smurf Attack, a type of DDoS amplification attack, but instead of using ICMP protocol, Fraggle uses UDP protocol to generate large traffic causing network congestion. Although outdated for modern systems, Fraggle Attack is still a typical example of DDoS attacks that utilize intermediate network infrastructure to amplify traffic.

Specifically, the hacker will send spoofed UDP packets to the broadcast address of a local network, targeting commonly used UDP ports such as Chargen (port 19) or Echo (port 7). When devices in the broadcast network receive this UDP packet, they will simultaneously respond to the spoofed IP address - which is the victim's IP. As a result, the target server is flooded with UDP responses and quickly paralyzed.

2.7 Slowloris

Slowloris is an attack against a web server, where an attacker uses the Slowloris tool to open hundreds to thousands of HTTP connections to the target server, then continuously drip-feeds HTTP headers but never completes the request. This forces the server to hold those connections waiting for the next data, exhausting the server's resources (threads/connections). When the number of connections reached the limit, the server will reject other valid requests, resulting in a denial of service (DoS) condition.

Slowloris allows attackers to overwhelm the system without affecting other services on the network

2.8 NTP Amplification

NTP (Network Time Protocol) attacks exploit publicly available NTP servers to generate massive amounts of UDP traffic against a target server. This attack is called amplification because the ratio of requests to responses can be as high as 1:20 or even 1:200. This means that any attacker with knowledge of a list of open NTP servers (via a tool like Metasploit or data from the Open NTP Project) has the ability to launch a massive DDoS attack.

2.9 HTTP GET

HTTP GET Flood is a type of application layer DDoS attack (Layer 7 DDoS), in this attack, bad guys often use botnets or automation tools to continuously send requests to specific pages (usually heavy pages, dynamic content). Each GET request requires the server to process, query the database or load images, CSS, JS,... This causes the server to consume CPU, RAM and bandwidth leading to serious performance degradation or complete shutdown.

2.10 Advanced persistent DoS (APDos)

APDoS is a form of denial of service attack that uses multiple attack vectors combined in a single campaign, reflecting current cybersecurity trends. When an attack occurs, the target can receive up to tens of millions of requests per second, targeting the "blind spots" of the organization and the service provider, attacking multiple layers of the network and data center in parallel.

APDoS uses multiple attack vectors combined in a single campaign

APDoS is not just a normal cyber attack, but an organized attack campaign, requiring businesses to invest comprehensively in security, both technology and human resources to deal with it. In an era where the Internet is a vital infrastructure, preventing APDoS is protecting the existence of businesses.

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3. Signs that you are under a DDoS attack

Early detection of a DDoS attack is key to minimizing damage and restoring service quickly. However, as DDoS attacks become more sophisticated, it is easy to mistake the signs of an attack for a simple system error. Here are some common signs that your system is under a DDoS attack:

• Website response is unusually slow or inaccessible
• Traffic spike from strange IP addresses
• Network bandwidth is consumed rapidly
• Server or CPU overload
• Unusual increase in HTTP requests
• Service connection errors like “503 Service Unavailable”

Not being able to access websites is a sign you've been under a DDoS attack.

4. Causes of a DDoS attack

Distributed denial of service (DDoS) attacks are becoming increasingly sophisticated and widespread, causing serious damage to many businesses, organizations, and even governments. Identifying the cause of a DDoS attack is an important first step in developing an effective defense strategy.

• Economic benefits: Attackers disrupt competitors' operations, damage brand image, and cause serious economic damage.
• Retaliation or personal harassment: Some attacks start from personal conflicts, disagreements within a company or between users. The attacker may be a former employee, a freelance hacker, or someone who had a relationship with the organization being attacked.
• Social, political, religious controversy: DDoS is also a tool used in digital protest campaigns, against specific policies, organizations or figures. Government websites, media outlets, and NGOs are easy targets.
• Attack for fun or fame: Many attacks are carried out just for fun, testing or to show off skills in the hacker community.
• Misdirection to penetrate the system: DDoS is used to distract and mask other attacks aimed at specific targets.
• Unfair competition: Attacks aimed at weakening a competitor's operations and reducing its competitiveness.
• Cyber ​​terrorism: DDoS can be used to disrupt and paralyze the information systems of key agencies.
• Using large scale botnets: Attackers use botnets — networks of malware-infected devices — to increase traffic and make it harder to detect.

DDoS attacks are common and varied with many different causes.

5. Instructions for preventing DDoS attacks

In the context of increasingly sophisticated DDoS attacks, system protection is not only a priority but also a must for every organization and business. Below are effective ways to prevent DDoS attacks recommended by experts for application in 2025.

5.1 Use high quality Hosting

One of the most basic but important steps is to choose a reputable hosting provider with strong infrastructure and anti-DDoS support.

Note when choosing:

• The provider should have dedicated firewalls, automatic traffic filtering systems.
• Ability to flexibly scale resources when traffic spikes.
• 24/7 support and built-in Anti-DDoS service.

Prioritize providers with good reputations, quick response to incidents, and clear SLAs.

👉 If you need to protect your system from anonymous cyber attacks, consider integrating an additional solution Hidemium high anonymous proxy to filter malicious traffic and hide real IP, helping to enhance overall security.

>>> Learn more: What is a Residential Proxy? A Tool for Online Privacy and Identity Protection 

5.2 Regularly monitor traffic

Website traffic monitoring is one of the most effective solutions to prevent DDoS attacks. Monitoring helps you promptly detect unusual behaviors such as:

• Sudden increase in traffic from a specific country or IP range
• Repeated requests to the same resource over a short period of time
• Traffic from invalid or spoofed IP addresses

Continuous monitoring also helps you ensure stable page loading speed and limit downtime, two important factors that affect your website on Google.

Monitor traffic regularly to detect DDoS attacks in time

✅ Pro Tips: Combine Hidemium proxy solution to anonymize real access sources and control traffic in and out of the system, helping to enhance proactive anti-DDoS capabilities.

>>> Learn more: Top 15 Trusted Free Proxy Sites

5.3 Blackhole Routing Setup

In the event of a DDoS attack, both legitimate and malicious network traffic can be routed into a “black hole” to be dropped from the network. This method, often considered the first line of defense, allows a website’s traffic to be blocked when the service is under attack.

However, the black hole routing process(blackhole routing), potentially dropping legitimate traffic. If not implemented properly, this method can disrupt legitimate traffic and allow attackers to leverage spoofed IPs to launch attacks.

5.4 Use a Website Application Firewall (WAF)

Web Application Firewall (WAF)is an important security tool that helps protect websites from DDoS attacks at the application layer – where attackers often exploit vulnerabilities by sending malicious requests such as SQL injection, XSS or HTTP Flood. WAF has the ability to filter and monitor traffic to the website, automatically Detect and block unusual connections, thereby preventing system overload.

In addition, properly configuring WAF also helps eliminate incomplete requests - a factor often exploited in Slowloris or HTTP GET Flood attacks. In addition, users should also combine WAF with additional measures such as limiting access speeds from suspicious IPs, configuring routers to prevent traffic storms, and using anonymous proxies such as Hidemium to enhance the security layer. Thanks to that, the system will maintain stable performance and Minimize damage from denial of service attacks.

Web application firewall (WAF) is a popular solution to prevent attacks

5.5 Spare bandwidth provisioning

Bandwidth provisioning is one of the simple yet effective strategies to mitigate the impact of DDoS attacks. When a system has a sufficient amount of spare bandwidth available, it can better absorb sudden traffic flows without causing immediate disruption to legitimate users. Investing in network infrastructure with more capacity than actual demand increases load capacity and ensures service availability in the event of an attack.

While not a sole defense, combining redundant bandwidth with other solutions such as web application firewalls (WAFs), CDNs, and dedicated DDoS protection services can help create a multi-layered defense system that can protect your website from all forms of denial of service attacks.

5.6 Access rate limit

Rate Limiting is an important security technique that helps prevent application-layer DDoS attacks by controlling the number of requests that each user or IP address can send to a server in a given period of time. Applying this limit helps prevent abnormal request flooding behaviors, such as HTTP Floods or Slowloris, which can overload system resources and disrupt services.

By restricting access, the system can eliminate or reduce invalid traffic, reducing load and improving resilience to DDoS attacks. However, it needs to be configured correctly so as not to affect the legitimate user experience. Therefore, flexible customization of the thresholds is important to ensure optimal protection while maintaining valid traffic.

5.7 Using Anycast Network Diffusion Method

Anycast Network Diffusion is one of the effective solutions to help disperse DDoS attack traffic across many different servers on the system. With a special routing mechanism, Anycast allows 1 IP address to be assigned to many servers in different geographical locations. When a user or attacker sends a request to this IP address, the traffic will be transferred to the nearest or least loaded server, helping to balance and reduce pressure on the system.

This method is especially useful in large-scale attacks, where malicious traffic can be split and absorbed by multiple network nodes instead of being concentrated on a single server. This increases load capacity, reduces the risk of overload, and maintains stable performance for online services.

6. What to do when under DDoS attack?

When a DDoS attack is detected, many businesses often have difficulty identifying the source of the attack or how to respond in a timely manner. In this case, the first thing you should do is immediately contact a cybersecurity expert or a reputable hosting service provider for in-depth technical support.

If you are unable to access a website or system resource, immediately notify your local network administrator to investigate and resolve the issue. Also, contact your Internet Service Provider (ISP) for appropriate troubleshooting instructions and possible measures such as blackhole routing or filtering of malicious traffic.

Above is all the detailed information about what DDoS is, common forms and effective DDoS attack prevention solutions in 2025. Hopefully the article from Hidemium will help you be more proactive in protecting your business systems and data. If you need in-depth support on secure proxies or IP anonymization solutions to combat cyber attacks, contact our team of experts immediately Hidemium for free consultation.

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