Internet is a global information system. Most of the users use search engines due to high volume of information in virtual world in order to access to required information. They often observe the results of first pages in search engines. If they cannot obtain desired result, then they exchange query statement. Search engines try to place the best results in the first links of results on the basis of user’s query. Web spam is an illegal and unethical method to increase the rank of internet pages by deceiving the algorithms of search engines. It involves commercial, political and economic applications. In this paper, we firstly present some definitions in terms of web spam. Then we explain different kinds of web spam, and we describe some method, used to combat with this difficulty.