SAN FRANCISCO — Did Facebook go too far this time?
Facebook sought to defuse a sharp backlash against the giant social network on Wednesday by publicly apologizing for running a psychology experiment on hundreds of thousands of people without their knowledge or consent.
Facebook's No. 2 executive, Chief Operating Officer Sheryl Sandberg, said the company communicated "poorly" about the experiment, which tested whether Facebook could manipulate users' emotions.
Her mea culpa came as British regulators said they had begun investigating the Facebook experiment.
Nearly a week after a report about the experiment appeared in the New Scientist magazine, the torrent of outrage shows no signs of abating. Protests have quickly spread on Facebook and social media.
"We are not experimental rats in a laboratory. What gives them the right to run experiments without our knowledge?" said Kiley Smith, a 31-year-old blogger and a daily Facebook user from Fairfax, Va. "I believe that is a personal invasion of privacy. They have definitely overstepped the bounds there."
In the week-long experiment, nearly 700,000 users were exposed either to positive or negative posts to see if the feelings would spread on the social network.
"The experiment manipulated the extent to which people were exposed to emotional expressions in their news feed," researchers wrote in their report. "These results indicate that emotions expressed by others on Facebook influence our own emotions, constituting experimental evidence for massive-scale contagion via social networks."
The research conducted with two universities was published in March.
"Given the massive scale of social networks such as Facebook, even small effects can have large aggregated consequences," the researchers concluded. "Online messages influence our experience of emotions, which may affect a variety of offline behaviours."
Facebook says it conducts this type of research to improve its service. It also says none of the information used was associated with a specific individual's Facebook account.
"This was part of ongoing research companies do to test different products, and that was what it was; it was poorly communicated," Sandberg said of the experiment, which was conducted in 2012. "And for that communication we apologize. We never meant to upset you."
But that has not mollified many users who say they were not aware that Facebook experimented on them or just how much power Facebook had to monitor and influence their behavior.
Denise Dorman, a 50-year-old writer, producer and digital content strategist from Carpentersville, Ill., says the experiment was "Orwellian."
"What's next? Will my bank lose my account balance for a day to test my reaction? Will big pharma start doling out placebos to unaware control groups for less serious maladies?" Dorman said.
Karl Volkman, chief technology officer of SRV Network in Chicago, says Facebook may not be able to shake its new public image as a digital age "Big Brother."
"If Facebook hasn't already crossed the line, they are getting very close," Volkman said.
Feeding the furor: the Facebook news feed — and what appears in it — was already a hotly contested subject.
People have strong feelings about the news feed. It's the main way they keep up with friends and family on Facebook.
Facebook filters the content in the news feed, and that has given rise to regular complaints that people do not see the updates they want to see.
Janet Cash, a 40-year-old middle school teacher from Davenport, Fla., says she relies on Facebook to stay in touch with far-flung family and friends and with subscribers to her newsletter. She says she has grown increasingly troubled that Facebook's computer algorithm decides what she sees in her news feed.
"I don't like Facebook manipulating my relationships," she said.
Grover Welch, a 42-year-old high school English teacher from Jonesboro, Ark., says he thinks it's more than that.
The revelation that Facebook was running tests on unsuspecting users has gotten many people to realize for the first time just how much power the giant social network has amassed, he said.
With nearly 1.3 billion users, Facebook has established itself as one of the primary means of communication and social interaction around the globe.
"People feel like they own what they put on Facebook, but they don't," Welch said. "We are investing all of our personal time into something that does not belong to us. This is the first time we have gotten a real glimpse of that."
And that — unlike previous flaps over privacy — has captured people's attention and shaken their faith in the service, Welch said.
"Finally people are seeing through the ruse," he said. "Facebook bills itself as being so user friendly, but they are not in it for us. This is a company, and we need to treat it like we do every other company. Everybody wants to feel like Facebook serves them, but it doesn't. Facebook serves Facebook and its investors. It has only its own self interest at heart."