Since more networking technologies and communication channels have been developed, Internet users have moved their roles from being strictly information consumers to both information consumers and producers. Moreover, users on nets might also be intermediaries, inter-actors, interferences or message providers, even service providers. Information on the Internet is dramatically growing. On one hand, it is good for all users to gain more information; on the other hands, it is getting more annoying to get too much information or too many messages daily. Some of them are useful, but the rest is annoying and useless. The useless information a user gets is often called "Spam". When a user is unwilling to receive spam, it is his/her privilege to reject it. Many self-service web services are applied to categorize the incoming messages through rough site policies, especially on email servers. Junk emails are classified and put into a folder of spam if it fits a specified filter. Thus...