Is the social network turning into an advertising network?

You may like Starbucks, but you'd never be in an ad for the company, right? You might be in one unawares -- on Facebook. On Tuesday evening the social-networking giant quietly rolled out a new advertising model that sells your activity -- your likes, your words and data about the places you visit -- as advertisements your friends see. 

They call it Sponsored Stories. Advertisers call it a godsend.

"If you can get your advertising into the activity feed, that's the best time to touch people -- and the launch of sponsored stories is doing just that," Vijay Pullur, CEO of social media marketing company SocialTwist, told FoxNews.com.

He pointed out that the move was completely expected in the advertising world -- inevitable even. But it may come as a shock to Facebook's 500 million users, who have unwittingly been clicking "Like" buttons across the Internet, unaware that they may be helping market and promote brands at the same time.

"From a user's perspective, it's a bit of a scarecrow. People are doing 'Likes' thinking it’s a personal thing, not a commercial thing," Pullur told FoxNews.com.

A Facebook spokeswoman downplayed the significance of the announcement, which the company unveiled to the advertising trade press.

"You will never see a Sponsored Story unless you would already see it in your news feed," explained Cyndi Schott, who handles public relations for Facebook.

In other words, if you write that you're enjoying a delicious Starbucks Mochachino, your friend will see that on his page and the coffee corp. won't pay a dime. Starbucks can also pay to feature your comment on your friend's page in a special widget, too.

It works the same way with Sponsored Stories others see from you, she added. "They would have to already be able to see them in their news feed.  So a Sponsored Story would only show up to users that were supposed to see the original post."

Since you would be seeing the information regardless, there's no way to opt out of the new advertising.

What about negative comments? Say you wrote that your Mochachino was horrible; will Starbucks use that as an ad? Facebook has developed a model for handling those comments an advertiser might not want associated with its brand, explained Ad Age magazine

Advertisers that don't want to take the chance of having negative sponsored stories pop up about them can buy only "likes," not all content. "As a marketer, you can say that I'm only going to do 'like' stories, since there is no way to change that," Facebook marketing lead Jim Squires told the magazine. "So you can figure out which is the best option for your organization."

Facebook has been in testing for three months and is launching with Coca-Cola, Levis and Unicef.

"Currently, marketers don't have the ability to know or plan word-of-mouth endorsements as part of their campaigns," Squires told the Wall Street Journal.

"This gives a way for marketers to increase the visibility of stories about their organization … this is word-of-mouth marketing at scale."

Jeremy A. Kaplan is Science and Technology editor at FoxNews.com, where he heads up coverage of gadgets, the online world, space travel, nature, the environment, and more. Prior to joining Fox, he was executive editor of PC Magazine, co-host of the Fastest Geek competition, and a founding editor of GoodCleanTech.