We describe a new type of threat to the Internet infrastructure, in the shape of a highly efficient but very well camouflaged click-fraud attack on the advertising infrastructure. The attack, which we refer to as a "badvertisement", is described and experimentally verified on several prominent advertisement schemes. This stealthy attack can be thought of as a threatening mutation of spam and phishing attacks, with which it has many commonalities, except for the fact that it is not the targeted individual who is the victim in the attack, but the unwitting advertiser.