There have been recent rumblings that the social network is more than the benign data dump it appears - last month, it used an algorithm to collate users' most popular photographs of 2014 into a cheery collage, and offended some by posting pictures of relatives who had died. Earlier last year, too, it caused outrage by allowing researchers to tweak newsfeeds for a sociological experiment.
But the latest development goes further still. Scientists from the Psychometrics Centre at the University of Cambridge have found, in a study of 86,000 Facebook profiles, that an individual's character can be predicted based on their "likes". Personalities are measured by the traits used in psychological assessments - openness, conscientiousness, extraversion, agreeableness and neuroticism - and the results forecast users' likely sexual orientation, political and religious views, life satisfaction and intelligence.
"Given that so much of our lives is lived through digital devices, all of them collecting information about you, it's a great opportunity for researchers to look at large numbers of people in more detail than ever before," explains Dr David Stillwell, co-author of the prediction software, entitled Apply Magic Sauce. "Some things about it are interesting and some are a little scary, in terms of what computers are capable of."
Anyone can take the free test, but reactions have been mixed. "It was fun to do," says one friend who let the software access her profile.
"But it says I'm nearly seven years younger than I am and that I'm single and [have a] 7 per cent probability of being a lesbian. I'm in a three-year relationship with a guy, so that's not quite right either."
In research, the test was able to predict personality traits based on just 10 "likes".
A preference for Doctor Who and the game Minecraft, for example, indicates a shy, reserved personality; liking gothic rock and Buffy the Vampire Slayer suggests emotional instability; while a fondness for tanning and meeting new people implies extroversion.
Accuracy improves as the "likes" increase (the average Facebook profile has 227). Seventy means the computer can identify sides to you that a friend couldn't; 150 puts it in a better place than a parent or sibling; and 500 enables predictions on a par with those of a spouse.
My profile doesn't have enough "likes" for the test - something of a relief, as my recent activity probably suggests I'm childish, perennially hungry and desperate for a holiday.
"You'll need to track down a trendy 20-year-old," suggests Dr Stillwell - so my colleague, Alice, acts as a guinea pig.
He has taken the test himself: "It says I'm very introverted. And it says I'm less open-minded than I would like to think I am - but colleagues say it's about right. It seems to know more about me than I do."
And there's the unsettling bit. The fact that social-networking behaviour can create such accurate personality portraits has raised concern.
"It is very Big Brothery," says Nathalie Nahai, a web psychologist and author of Webs of Influence.
"There is much more intimate surveillance online than people know about, and it's crucial we understand that we have a choice - and what we're giving up by opting in. If we're seduced by the convenience of these networking platforms, I worry we'll sleepwalk into giving up more information than we intend."
Any research in this area is, inevitably, limited by the disparity between our online and offline personalities - Facebook profiles tend to reflect an idealised image ("liking" that cool band, for example, or using a flattering profile picture).
But Dr Stillwell insists this doesn't undermine his study. "Of course there are issues about self-presentation, but it's a bit like applying for a job. Even if everyone presents themselves as being more conscientious or agreeable than they are, the most and least conscientious or agreeable will still rank in the same place in their social group."
So should you take the Facebook test? It's a bit of harmless fun, and should be understood as such.
"But be careful," warns Nahai. "Something as throwaway as a 'like' can give away rich personal information that you can't get back once it's in the public domain."
Worth bearing in mind next time your cursor hovers over that little, innocuous thumbs-up.
To take the test, log in to Facebook, open a new tab and search for applymagicsauce.com/test. Then click on 'Predict my Profile'
Case study
Finding out that you're unhappy, neurotic and a bit thick - well, it's not the ideal start to a day, is it?
These, sadly, were the results of my dalliance with Apply Magic Sauce, the Facebook test that "translates individuals' digital footprints into detailed psychological profiles". Or, rather, "looks at a few of your Facebook likes and destroys any self-esteem you ever had".
My personality predictions were as follows:
Age: 26. Wrong. I'm 25, as stated on my Facebook page.
Psychological gender: 46 per cent masculine. Wrong. I may have more male friends than female, but I'm no tomboy.
Sexual preference: 5 per cent probability that I'm lesbian. Not to my knowledge.
Relationship status: 50 per cent probability that I'm single. Right. But considering the number of dating websites I've liked, I'd have expected greater accuracy.
Personality: 51 per cent conservative and traditional; 51 per cent spontaneous and flexible; 52 per cent shy and reserved; 32 per cent assertive and competitive; and 50 per cent emotional and stressed. All wrong. I disagree, but then I would, wouldn't I?
Education: 15 per cent probability of having studied art. Wrong. I'm not artistic in the slightest.
Political orientation: 42 per cent Liberal. Wrong, I'm Conservative.
Religious orientation: 38 per cent none. Wrong. I'm Christian, though not overly active.
Life satisfaction: 50 per cent. Wrong. Life has never been better. I'd put it at 85 per cent.
Intelligence: 55 per cent. A little harsh - I'm not Stephen Hawking, but I did get my fair share of As.
The site hedges its bets and says that the test "may not be an entirely accurate picture of who you really are". I couldn't agree more.
