What is the ruling on exchanging clicks on ads (traffic exchange) to earn profit from YouTube and AdSense?

The question contains two rulings: the first is the permissibility of earning from displaying advertisements, as long as they are free from unlawful content. The second is the impermissibility of agreeing with colleagues to exchange clicks on advertisements, due to the deception and fraud involved towards the advertisers. This is supported by the Prophet's (peace and blessings be upon him) saying: "Whoever deceives us is not of us, and cunning and deception are in the Fire." This forbidden act must be avoided, and one should seek lawful earnings.