1. Bandwidth Attacks: Loading any website takes certain time. Loading means complete webpage appearing on the screen and system is awaiting user's input. This "loading" consumes some amount of memory. Every site is given with a particular amount of bandwidth for its hosting, say for example, 50 GB. Now if more visitors consume all 50 GB bandwidth then the hosting of the site can ban this site. The attacker does the same - he/she opens 100 pages of a site and keeps on refreshing and consuming all the bandwidth, thus, the site becomes out of service.

2. Logic Attacks: ,These kind of attacks can exploit vulnerabilities in network software such as web server or TCP/IP stack.

3. Protocol Attacks: Protocols here are rules that are to be followed to send data over network. These kind of attacks exploit a specific feature or implementation bug of some protocol installed at the victim's system to consume excess amounts of its resources.

4. Unintentional DoS Attack: This is a scenario where a website ends up denied not due to a deliberate attack by a single individual or group of individuals, but simply due to a sudden enormous spike in popularity. This can happen when an extremely popular website posts a prominent link to a second, less well-prepared site, for example, as part of a news story. The result is that a significant proportion of the primary sites regular users', potentially hundreds of thousands of people, click that link within a few hours and have the same effect on the target website as a DDoS attack.