1. Reputation System
Reputation is the opinion of the public toward a person, a group of people, or an organization.
Reputation system computes and publish reputation scores for a set of objects(e.g. products, services, goods or entities) within a community or domain, based on a collection of opinions that other entities hold about the objects.

In particular, in ebay system, user left feedback for each other after each transaction.
These feedback scores accumalate into the reputation score.
Then the reputation score assisted people make  decision making.

Typical Reputation system included:

Because its influence in decision making for users, fraudsters tend to gain extra reputation scores by creating a large number of pseudonymous entities.
There is a jargon the describe the attack — Sybil Attack.

2. Sybil Attack
“Sybil” represents dissociate identity disorder.
It orginates from a 1973 book about Ardell Mason’s treatment for dissociative identity disorder.
The Sybil attack is an attack wherein reputation system such as P2P networks. It attacks by register many times with multiple identities and then control enough of the space to capture particular traffic.

The key techniques to prevent sybil attack is validate techniques to make sure a one-to-one map between user and account.
Techiniques such as cerirification authority and weak secure IDs can be used.

3. Wait a minute, what’s the connection between you and your research?
The sybil attack or some variaties existed in many different scencerio with different names.
Two meathods to deal with the attack
- Prevention. Validate user’s identify by cerirification authority or weak secure IDs(e.g.IP) to prevent sybil attack.
- Detection. Once Sybil attack had occured, how can we detect them?
Attack detection is what I really want to deal with.

4. Related Work and their techniques
* Spam Detection in Web Graph
Web graph is a reputation system which link represents support to a web page.
In the web search area, there are many mature techniques to define the reputation score(e.g. PageRand and HITS).
Reading List:
Jian Pei, Bin Zhou, Zhaohui Tang, Hai Huang. “Data Mining Techniques for Web Spam Detection“. In Proceedings of the 12th Pacific-Asia Conference on Knowledge Discovery and Data Mining (PAKDD’08), Osaka, Japan, May 20-23, 2008.
* Data Conflict Resolution

References:
[1] “Sybil”,”Sybil attack”, “Reputation System”in Wikipedia
[2] Security and Trust part of Joseph M. Hellerstein’s slide Tutorial: Architectures and Algorithms for Internet-Scale (p2p) Data Management. VLDB 2004.

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以下是八卦(搜这个太花时间了，以后要克制好奇心，至少要延缓一下好奇心)
Sybil: (西比尔)另一个意思: 女预言家,常写作Sibyl,希腊语。Harry Potter中的占卜课老师就叫做Sibyl Trelawney.

关于她的传说, Sibyl是希腊神话中阿波罗神庙的女祭司，由于受到太阳神的眷顾而具有了预言未来的能力。
她拥有像沙子一样多的寿命，这是她要求阿波罗给她的，但是她忘了要求青春，以至于她后来唯一的渴望就是死。
(T.S.Eliot的长诗《荒原》的题记，“孩子们问西比尔要什么，西比尔回答：‘我要死’”)

后面一段貌似在某篇奇幻小说中看过。