P2P分享系統可有效快速的在網路上分享各種檔案，其中卻也充斥著許多未授權檔案的分享以及侵權的行為。近年來世界各國不留餘力抵制P2P網路上的侵權行為，為此可以說是不惜採用激烈手段。但不可否認的，以P2P網路為主的檔案分享系統依舊是極具效率的，若此後P2P網路往分享授權檔案和使用者付費的方面繼續前進，相信P2P分享系統為最佳選擇。P2P網路上的檔案汙染問題已在2005年Infocom會議上提出。雖此問題之造成是針對P2P網路分享侵權軟體所做的反擊，但若將來P2P網路上所分享之檔案都得到合法授權後，防制汙染就為一門重要的課題。
受汙染檔案(Polluted Files)，是指內容與標題不符的檔案或是檔案某部分為損壞或滲入不屬於此檔案的資料。P2P網路中得檔案安全性是相當低的，除非已下載此檔案否則將無法辨別此檔案的正確性。
本研究使用RAID上的容錯機制來增加檔案的安全性，使其被汙染時可自行復原原始資料。此容錯機制可有效地抑制汙染，使一個受攻擊中P2P網路正確檔案擷取率上升，並在短時間中將P2P網路分享環境復原。

An Infocom 2005 paper exposed and investigated the pollution problem of the P2P file sharing system. Nowadays, there are too many illegal files in any kind of Peer-to-Peer file sharing systems. It is unstoppable to avoid using the P2P file sharing system, because sharing a file in the p2p network is the most efficient way to spread a file around. We could hear about a lot of assumpsits against all kinds of P2P software by companies who have the copyright about files that are shared. And then, it must be a trend that if you want to share files, they must be authorized files. Thus, it is an important problem about polluted files.
How to propose an anti-pollution mechanism in the P2P network is important in the future. Polluted files are files whose content have be polluted. Content pollution is the most common form of pollution currently. P2P networks are vulnerable to pollution attacks, and files have no way to protect themselves. We cannot recognize if a file is a decoy unless you download it. There are less ways to make sure your downloading file is correct. When we got a polluted file, we just search another file and restart the download in most time.
This thesis proposes a fault tolerant mechanism to improve the safety of a sharing file. It can efficiently decrease files that are polluted and recover the environment of the P2P network from attacked in a short time.

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