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In page Advertising:
"Online advertising began with unsolicited bulk e-mail advertising known as "e-mail spam". Spam has been a problem for e-mail users since 1978.[4] As new online communication channels became available, advertising followed. The first banner ad appeared on the World Wide Web in 1994.[5] Prices of Web-based advertising space are dependent on the "relevance" of the surrounding web content and the traffic that the website receives.[citation needed]