Where do these sites get their money?

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I have been wondering about this, we see many more people doing these paid to click, paid to read, paid to sites and survey sites. Now many more sites are becoming like mylot. With the economy the way it is, people getting laid off, more people trying to earn money from home......where is the money coming from to pay us? I know some are paid from the advertisers but if they cut down on advertising? then what? Just curious....