Entrecard AdSense TOS

"Sorry to burst your bubble, but if you're using Entrecard and AdSense together then you're probably lucky to still have your AdSense account. The reason: AdSense and Traffic Exchange Programs together break the rules of Adsense. It just so happens that Entrecard is a Traffic Exchange Program. Therefore, Entrecard users are breaking the rules of AdSense when they use the two programs together."

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Source: Video Blogging Tips