"Viral marketing" has been used as a catch-all term for word of mouth marketing, buzz marketing, stealth and guerilla marketing, grassroots marketing and influencer marketing. Though many in the industry resent being lumped in with all of these different types of marketing, it is all marketing - and advertising - just the same. For direct marketers, that means being aware of applicable legal obligations before embarking on such campaigns. A little knowledge can save you from a legal or public relations nightmare.