Paid search advertising has not been without controversy and the issue of how search engines present advertising on their search result pages has been the target of a series of studies and reports by Consumer Reports WebWatch. The Federal Trade Commission (FTC) also issued a letter in 2002 about the importance of disclosure of paid advertising on search engines, in response to a complaint from Commercial Alert, a consumer advocacy group with ties to Ralph Nader.
Digital marketing is the marketing of products or services using digital technologies, mainly on the Internet, but also including mobile phones, display advertising, and any other digital medium. Digital marketing channels are systems based on the internet that can create, accelerate, and transmit product value from producer to the terminal consumer by digital networks.
When would this be useful? If your site has a blog with public commenting turned on, links within those comments could pass your reputation to pages that you may not be comfortable vouching for. Blog comment areas on pages are highly susceptible to comment spam. Nofollowing these user-added links ensures that you're not giving your page's hard-earned reputation to a spammy site.
Digital marketing is defined by the use of numerous digital tactics and channels to connect with customers where they spend much of their time: online. From the website itself to a business's online branding assets -- digital advertising, email marketing, online brochures, and beyond -- there's a spectrum of tactics that fall under the umbrella of "digital marketing."