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Internet has evolved from a small scientific network carrying data between trusted computers to the ubiquitous communications infrastructure we have today, carrying all types of traffic, including data, voice, video, and financial transactions. In this new environment, users may have conflicting interests and/or malicious intentions, launching various kinds of attacks against innocent hosts and/or the networking infrastructure. 
During the past few years P2P (Peer to Peer) got attraction of the Internet users. The term P2P describes the concept of a network of equals (peers) using appropriate information and communication systems, able to spontaneously collaborate without necessarily needing central coordination. In contrast to client/server networks, P2P networks promise improved scalability and lower ownership costs; they are self-organized and involve decentralized coordination of previously underused or limited resources; they have a greater fault tolerance, and offer better support for building ad hoc networks.
The main use of P2P by the public is to share and access music, movies, documents and software.. As a result, governments are interested in the areas of copyright, intellectual rights, and privacy whereas Internet service providers (ISPs) are interested in how much bandwidth is being used and and who is responsible for it, and of course the music industry is interested in profits or losses as a result of file sharing. General public tends to be interested in is how to get free stuff, quickly, and safely.
Currently P2P technology such as BitTorrent, Gnutella, Napster, Freenet, and Morpheus provides users with stores of music, movies, software, and literature to download for free. However P2P technology is not limited to free downloading only; Voice over P2P (VoP2P) is another compelling application of P2P technology  also being used widely. E-commerce could benefit from P2P as well. Members of B2B exchanges could use P2P to cut out the middlemen that serve them; such exchanges could become a whole lot more profitable for buyers and sellers.
Due to the design of P2P it is very hard to monitor the traffic for each user, and as the technology develops it is only going to get harder. P2P application developers are continuously changing the techniques to bypass the files’ free files and other countermeasures.
1. P2P overlay routing protocols
Initially Napster, a centrally managed P2P network, as very popular, and then Gnutella, Kaaza, and Bittorrent followed it with some structural changes, as these P2P networks were designed as loose structures, highly dynamic, without any central control or authority, internationally. Due to its self-organization and the loose federation structure of continuing dynamic organization, these have become insecure and present very challenging security issues in expanded networks.
2. P2P file-sharing risks
P2P file-sharing software may cause severe damage to personal systems or corporate networks. This type of file sharing can overload networks and create a tremendous strain on them, interfering with other users' ability to connect to the Internet for research and informative purposes. P2P software is often configured in such a way that other users can access hard drives and share files all of the time. Most of these also come bundled with adware and spyware applications, allowing third parties to monitor individual’s Internet usage and send advertisements to computers even when a user is not using a file-sharing program. This kind of activity degrades the computer's performance and monopolizes additional network bandwidth. Downloading from this type of file sharing may contain viruses which can infect the individual system or network; some viruses are designed specifically to spread through P2P networks.
Therefore installation and utilization of file-sharing utilities may lead to misuse of the security of secret data owned by the organization or individual.
3. Security threat
Users are usually unaware of the fact that files may contain malicious codes which may harm the system while downloading files from unknown source. These sorts of applications may also be spread by attackers to target systems or networks. Attackers or hackers may spread viruses, adware, worms or Trojan horses through the files, which can damage or steal information from the victim’s system or network.
Considering the weaknesses inherent to the centralized architecture of current C&C botnets, it is a natural strategy for botmasters to design a P2P control mechanism into their botnets. In the last several years, botnets such as Slapper, Sinit, Phatbot, and Nugache have implemented different kinds of P2P control architectures.
Some of the P2P applications may ask the user to open certain ports, which can prove dangerous and that network can be compromised. These types of action make networks vulnerable the networks, networks which can eventually be victimized by hackers through a particular open port.
Downloading suspicious files from unreliable sources may cause a significant amount of traffic over the network as a resultant of the unavailability of the particular network or system. This unexpected heavy traffic may also reduce the availability of certain programs on a computer or may limit access to the Internet.
Based on discussion above P2P has become regulatory concern and it should be considered during the policy-making process
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