A fake blog (sometimes shortened to flog or referred to as a flack blog) is an electronic communication form that appears to originate from a credible, non-biased source, but which in fact is created by a company or organization for the purpose of marketing a product, service, or political viewpoint. The purpose of a fake blog is to inspire viral marketing or create an internet meme that generates traffic and interest in a product, much the same as astroturfing (a "fake grassroots" campaign).

Fake blogs are corrupted forms of public relations, which as a discipline demands transparency and honesty, according to the Public Relations Society of America's code of ethics and the Word of Mouth Marketing Association's code of ethics. Authenticity and transparency are important in social networking and blogging, as these codes of ethics attest.

As social networking tools gain in popularity, corporations and special-interest groups legitimately use their own blogs to promote company agendas without cloaking their identities (one such example is http://www.blogsouthwest.com, a blog sponsored by Southwest Airlines and written by its employees).

One notorious example of identity cloaking, resulting in a fake blog, was exposed when Edelman, an international public relations firm, created a fake blog in 2006 called Walmarting Across America. It was purportedly written by two Wal-Mart "enthusiasts" who decided to journey across the United States in an RV, blogging about the experience as they visited Wal-Marts along the way. While two people actually did travel across the United States in an RV, the publicity stunt was revealed to be paid for by Wal-Mart, a client of Edelman.

In this way, a fake blog is akin to industry-supported "astroturf" efforts that pose as legitimate grassroots activity, as identified by groups such as PR Watch, which investigates the origins of so-called grassroots organizations.