The privacy dangers of Google go beyond what Google knows about you -- you may have given dozens of sites access to your Google account information without realizing it. Here's how to conduct a security audit of your Google account, and how to take action to keep it safe.
There are a number of reasons you might have given a site access to your Google account. You may have wanted to log into the Web site to gain access to its services or information, and rather than setting up an entirely new account there, you instead decided to use your Google log-in. Or you may want the site's services to connect with your Google data. But when you do either of those, you might not necessarily have realized what kind of information about your Google account that you agreed to let the Web site see. And if you're like most people, you probably try out plenty of Web sites and services, and then end up stop using them, sometimes after the very first visit.
So how do you see what sites have access to your Google account, and what kind of information they can get? First log into any Google service you use, such as Gmail or Google+. Then click your account picture and click the "Account" link in the pop-up that appears with your account picture.
You'll be sent a page with information about your account. Look across the top of the screen. You'll see a Security link. Click it.
Look on the page for "Account permissions" section, then click "View all." That brings up a list of all the accounts outside of Google to which you've granted permission to access your account. Don't be surprised if it's quite long. Mine, for example, has nearly three dozen entries -- everything from my Android devices to my iPhone and iPad, my Barnes and Noble account, a number of services I use regularly, and quite a few I rarely use, if ever. And there are also several that I don't recall using at all.
Click any and you'll get the rundown about the account, including what Google account information the service can access. So, for example, some sites may only be able to view very basic account information, such as your email address, in order to log you in. But other sites may have far more access -- for example, access to your contacts and the files and documents in your Google Drive.
What you do next couldn't be simpler. Click on a site, and at the right-top of the screen click "Revoke access." That's all it takes. You've just taken away access to your Google information from the site.
I recommend doing a sweep of your Google account like this regularly. You'd be surprised at how many services you sign up for and then forget.