Introduction

A denial-of-service (DoS) attack is an attempt to make a machine or network resource unavailable to its intended users, such as to temporarily or indefinitely interrupt or suspend services of a host connected to the Internet.

A distributed denial-of-service (DDoS) is where the attack source is more than one and often thousands of IP addresses.

Criminal perpetrators of DoS attacks often target sites or services hosted on high-profile web servers such as banks, credit card payment gateways; but motives of revenge, blackmail or activism can be behind other attacks.

Symptoms

Symptoms of denial-of-service attacks including:

• Unusually slow network performance
• Unavailability of a particular website
• Inability to access any website
• Dramatic increase in the number of spam emails received (e-mail bomb)
• Disconnection of a wireless or wired internet connection
• Long term denial of access to the web or any internet services

Denial-of-service attacks can also lead to problems in the network 'branches' around the actual computer being attacked. For example, the bandwidth of a router between the Internet and a LAN may be consumed by an attack, compromising not only the intended computer, but also the entire network or other computers on the LAN.