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Unwitting Collaborators, Part 7: Denial-of-Service Attacks

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Many supposedly "secure" sites - even including major Internet providers - have suffered from denial-of-service (DoS) attacks. Frank Fiore and Jean François tell you how to avoid being a victim.
Read the introduction to this article series.
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Introduction: What is Denial-of-Service (DoS)

A denial-of-service (DoS) attack (also referred to as a distributed denial-of-service or DDoS attack) is an attempt by a malicious person or organization to prevent legitimate users from using a network service. The DoS attack can take several forms:

  • "Flooding" a network with constant requests for service, preventing legitimate network traffic from reaching a service

  • Disrupting connections between two machines, resulting in the prevention of access to a service

  • Preventing a particular individual from accessing a service

  • Disrupting service to a specific system or person

These attacks are becoming more and more sophisticated, and in some cases the denial of service may be part of a larger attack, or used to conceal the real attack that may be in progress—or soon to come. Some attacks even can be performed through the illegitimate use of resources such as an FTP site. A malicious intruder may use an anonymous FTP area to store popular information such as illegal copies of commercial software. When this information is announced, the traffic generated by the many users accessing the FTP site could generate an immense increase in network traffic.

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