Most common types of spam:
Doorway pages: They reduce the quality of the search engine result and are irritating to their users.
Mirror sites: Mirror sites are the replication of another internet site that uses different keywords.
Hidden text: Hidden text also known as search spam, are generally readable to search engine spiders but they are invisible to visitors.
Note: - If everyone takes the preventive measures, then spammers will soon realize that their useless mails are no longer attractive to the viewers.

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