It was enough to make the milk in their cappuccinos curdle.

Customers at a coffee shop in the U.K. learned they could get a free drink if they liked its Facebook page. They reacted with bemusement when baristas handed them drinks with data like their names, ages, jobs and living addresses written on the cups.

That information was gleaned by not-for-profit Cifas, which filmed their reactions with hidden cameras.

Granted, not every coffee shop's Facebook page has a small army of data experts combing the internet while a barista steams some milk.

But the message is clear: many people's personal information — probably more than they realize — is online and searchable by anyone from nosy neighbours to co-workers to identity fraudsters.

Apps aren't really free

Anita M. McGahan a professor at the Rotman School of Management at the University of Toronto, says the video is a good reminder of how much personal information we give out in order to use social media and other modern apps.

"In exchange for all these quote-unquote free services, such as the ability to stay in contact with our friends on Facebook, that freedom isn't really free," she told CBC News. "What you're paying with is information about your identity."

You local barista probably won't find this info when you buy a latte. But data like hometown, profession, email address and more are easily searchable if you don't check your privacy settings on Facebook. (Evan Mitsui/CBC)

Ann Cavoukian, executive director of Ryerson University's privacy and Big Data Institute and former Ontario information and privacy commissioner, often talks to students in middle or high school about how best to control the flow of information on their most commonly used apps.

"They're clueless that the information they provide online may lead people back to their physical homes," she says of young digital natives.

But once they're armed with the right knowledge, "they know exactly what to do. They know how to protect their data better than I do."

Facebook's Help Center has a comprehensive guide to the privacy options available to users. You might want to keep it bookmarked for an occasional refresher. (Facebook)

"I think people should regularly, at least a few times a year, take a look at all the permissions, and all the privacy settings that they have in all of these apps, and think about whether they're comfortable with them," privacy and tech lawyer David Fraser told CBC News.

He specifically mentions Twitter's ability to tag users in other people's tweets or photos, as well as tagging a tweet's location, using a smartphone's location capabilities to share where you sent a tweet. Both can be turned off.

"We live in a busy world and a busy society, but it's really to their benefit, a couple of times a year, to set aside half an hour and think about these sorts of things." he advises.

Facebook privacy settings: Here's where to start

On desktop computers, Facebook users can take a privacy checkup by clicking on the small padlock icon on the top right of their screen. It'll ask you some basic questions about your profile, including who can see your posts (Friends? Anyone in the public? Only you?). It also asks who can contact you. For instance, you can restrict future friend requests to friends of your friends.

If you want more nuanced control of your privacy settings, however, you'll have to click on the small triangle right next to the padlock. It's the menu that also includes links to creating groups, ads or simply logging out of Facebook.

Click on settings, and take a look at the privacy link on the left side of the menu for an expanded version of the privacy checkup menus.

Facebook users can try the privacy checkup to choose who sees your posts and which third-party apps have access to your profile, but you'll need to go deeper into the menus for full control. (Facebook)

There are separate settings to configure who sees posts you make in the future, as well as "past posts" or anything you've posted before the last time you tinkered with these settings.

You can also toggle whether your Facebook profile can be found by outside search engines. Turn this option off and no one will be able to find embarrassing photos with a simple Google search.

Facebook's Help Center also includes a section on privacy basics, with a pretty extensive guide to all the privacy settings available to a user. Think of it as an instruction manual for Facebook's basic functions. It doesn't hurt to keep it bookmarked.

When in doubt, just don't post it

For all of the settings, tutorials and app functions users can tinker with, however, there's no avoiding the fact that once something's out there on the internet, it's very hard to make it disappear forever.

For tech columnist Peter Nowak, safer is better than sorry. That comes with posting photos, status updates about where you are, and common profile data like your birthday and hometown.

"I think your default setting when using these services is don't trust them at all," warns Nowak. "You can't really trust Facebook or other social media companies to guard your information. You need to have common sense and be careful about what you put out there in the first place."