A dating website has admitted "experimenting" on unsuspecting love-seekers by setting them up with "bad matches" to test its technology.
New York-based site OkCupid, which has 30 million worldwide users including 700,000 in the UK, made the admission in the first post for three years on its blog site OkTrends.
It provoked a backlash online and comes after Facebook faced criticism over a psychological experiment along with two US universities to alter news feeds of almost 700,000 users and monitor their reactions.
In the blog, co-founder Christian Rudder defended the action by claiming that experiments were necessary to test the site's ability to match potential partners.
He said: "We noticed recently that people didn't like it when Facebook "experimented" with their news feed. Even the Federal Trade Commission (FTC) is getting involved.
"But guess what, everybody: if you use the internet, you're the subject of hundreds of experiments at any given time, on every site. That's how websites work."
The site, which is free to join, asks users to answer a series of questions and uses algorithms to match them to others, providing the result as a percentage.
In one experiment users who were a bad match, with a percentage of 30%, were told they would be good for each other - a 90% match. It resulted in those couples making contact more often.
Mr Rudder, a Harvard maths graduate, concluded: "When we tell people they are a good match, they act as if they are. Even when they should be wrong for each other."
In other tests, the firm ran profiles with pictures only, hiding the accompanying text, and found users responded solely to the picture, so much so that Mr Rudder declared: "Your picture is worth that fabled thousand words, but your actual words are worth...almost nothing."
But the practices have been greeted with criticism online, not least in the comment section on the blog post entitled "We Experiment on Human Beings".
Jeff Trigger said: " People signed up expecting you all to be truthful. You weren't. It's not funny, and even worse it could have been dangerous. If you want to perform science experiments, go to school. "
Sheri Young added: "G uess you've lost some credibility!"
And Bernie Hogan, chairman of the ethics review board at the University of Oxford's Internet Institute, told the Times the experiment would not have been approved by his board.
"Some users are being exploited," Dr Hogan said.
OkCupid, which launched in 2004, is owned by media conglomerate InterActive Corp (IAC), which also owns similar dating sites such as Match.com and the Tinder mobile app.