No longer. While traditional "paid" media -- such as television commercials and print advertisements -- still play a major role, companies today can exploit many alternative forms of media.

The way consumers now approach the process of making purchase decisions means that marketing's impact stems from a broad range of factors beyond conventional paid media.

The rough guide to marketing success used to be that you got what you paid for.

Consumers passionate about a product may create "earned" media by willingly promoting it to friends and a company may leverage "owned" media by sending e-mail alerts about products and sales to customers registered with its Web site.

But in some cases, one marketer's owned media become another marketer's paid media for instance, when an e-commerce retailer sells ad space on its Web site.

We define such sold media as owned media whose traffic is so strong that other organizations place their content or e-commerce engines within that environment.

Paid and owned media are controlled by marketers promoting their own products. For earned media, such marketers act as the initiator for users' responses.

Besides generating income, the presence of other marketers makes the site seem objective, gives companies opportunities to learn valuable information about the appeal of other companies' marketing, and may help expand user traffic for all companies concerned.

This trend, which we believe is still in its infancy, effectively began with retailers and travel providers such as airlines and hotels and will no doubt go further.

Johnson & Johnson, for example, has created BabyCenter, a stand-alone media property that promotes complementary and even competitive products.

The same dramatic technological changes that have provided marketers with more (and more diverse) communications choices have also increased the risk that passionate consumers will voice their opinions in quicker, more visible, and much more damaging ways.

Such hijacked media are the opposite of earned media: an asset or campaign becomes hostage to consumers, other stakeholders, or activists who make negative allegations about a brand or product.

Members of social networks, for instance, are learning that they can hijack media to apply pressure on the businesses that originally created them.

If that happens, passionate consumers would try to persuade others to boycott products, putting the reputation of the target company at risk.

In such a case, the company's response may not be sufficiently quick or thoughtful, and the learning curve has been steep.

Toyota Motor, for example, alleviated some of the damage from its recall crisis earlier this year with a relatively quick and well-orchestrated social-media response campaign, which included efforts to engage with consumers directly on sites such as Twitter and the social-news site Digg.