Facebook and Google make billions of dollars selling access to the most valuable commodity in the world: You. 

You've probably heard the adage that if the service is free, you're the product. It's catchy, but it's not true. In reality, the cost of using these "free" services is your privacy.

Facebook regularly claims that advertising is necessary to keep Facebook free for everyone. You provide your most valuable asset to these companies in exchange for services that exist primarily to feed you advertising. 

While Facebook and Google have started to talk about shifting their practices to better respect your privacy, here are four things they don't want you to know, and what you can do about it:

They know way more than you think.

Google knows what you search for online, where you travel, what's on your calendar, who you take photos of, who your contacts are, which ads you click on and what you buy. For a lot of you, that's more than your spouse or partner knows. 

Facebook is the same, only it doesn't have to guess based on your activity. You told the company. You put it on your profile and posted the photos of your family on vacation. You tagged the location and everyone in it.

Both Google and Facebook track everything within the ecosystem of their platform, and sometimes even once you leave. Facebook, for example, tracks which of their advertisers' sites you visit after you leave their site, so it can serve you ads when you return. 

There's no question that if most of us had any real concept of how much of our personal information was being captured and stored, we'd feel differently about whether it's really worth it.

They make it as hard as possible.

Both companies have talked recently about giving you more control over your privacy, and have released updates that they claim are designed to do that. Facebook has dozens of security and privacy settings that are supposedly meant to give you control over every aspect of your experience.

The truth is, by requiring you to make so many changes, most people just ignore it all. That means you're probably using Facebook's default permission setting to let it scoop up your information. 

This has real consequences. Just last month, it was revealed that more than 500 million Facebook user records were potentially exposed by third-party developers that had access to personal data when they were posted to Amazon's cloud computing service without any security or encryption. And the company is currently the subject of a federal criminal investigation over data-sharing deals.

Google is the same way. Despite the recent announcement that it will let users automatically delete their history after three or 18 months, you still have to know it's an option, navigate through the settings, and then make the changes.

Most people simply won't. Google knows this--in fact, they design it that way. They would rather you not take the initiative to change anything about your relationship with them because that makes it harder for them to make money.

They could make it easy but they won't.

Both companies could provide a simple "opt-in" for collecting your information. This would be easy to implement.

Think about when a new app on your iPhone wants to use your location. It has to ask for permission and explain generally why it needs this information. It gives you a choice and it can't use your personal information without your consent. 

Facebook and Google won't because it makes no sense for them. If everyone chose not to opt-in, both companies would cease to exist as profitable enterprises.

They don't have your best interests in mind.

Since both Facebook and Google exist to generate a profit for their shareholders, they have to maintain as much access to your personal information as possible, without stirring up an uproar. That means that invading your privacy is big business. Really big business.

The two companies are already the two biggest advertising platforms in the world, and there is simply no way to avoid the conflict of interest between targeting you with ads and respecting your privacy. Never mind the possibility of your information being accessed by bad actors, Google and Facebook literally feed on your privacy.

Give Facebook credit for allowing you to delete off-site activity, so it can't be used for targeted ads, but at the same time, they've started letting advertisers target you with ads based on where you've previously been.

What you can do about it.

You could take the dramatic step: Shut down your Facebook account and stop using Google. Chances are, however, you'll probably do what most people do. Nothing. 

Then again, if protecting your privacy is important to you, there are a few things you can do. Both companies do offer guides on managing your privacy settings. Facebook has a help article that covers their settings that is a good place to start. Likewise, Google will walk you through changing your settings for many of their products. 

Finally, if you're using Chrome, sign out of your Google account when browsing or use Incognito mode. That will prevent Google from keeping track of your search history and clears your browser content when you close the window.

For example, I've been using a Google Pixel 3a for the last two weeks, and the first thing the phone asks you to do is to sign in with your Google account, which seems super convenient. Then I realized that maybe I don't want my phone constantly sending everything I do on my phone back to Google.

At least on my iPhone, most of the sensitive information is encrypted on the phone and Apple claims they can't access it even if they want.