Security

Take a Deep Breath: A Stealthy, Resilient and Cost-Effective Botnet Using Skype

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Executive Summary

Skype is one of the most used P2P applications on the Internet: VoIP calls, instant messaging, SMS and other features are provided at a low cost to millions of users. Although Skype is a closed source application, an API allows developers to build custom plugins which interact over the Skype network, taking advantage of its reliability and capability to easily bypass firewalls and NAT devices. Since the protocol is completely undocumented, Skype traffic is particularly hard to analyze and to reverse engineer. The authors propose a novel botnet model that exploits an overlay network such as Skype to build a parasitic overlay, making it extremely difficult to track the botmaster and disrupt the botnet without damaging legitimate Skype users.

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