Negative advertising or “poisoning the well” is the practice of attacking a competitor or opponent to make yourself look more credible. The logic behind the practice is that if the other party's reputation is damaged, you end up looking better. While poisoning the well is de rigeur in political advertising, businesses also use it as a part of their overall advertising strategy. It’s particularly popular in the tech industry, where rivalries tend to run deep. This smear tactic technique is also frequently used by a second or third tier competitor as a way to try to tarnish the market leader’s image. Below outlines a couple google examples of negative advertising.
Scroogled (Courtesy of Microsoft)