No matter which browser you prefer—Chrome, Firefox, Edge, Safari, Opera, or any of the others—it will almost certainly offer an incognito or private mode, one which ostensibly keeps your web browsing secret. (Google Chrome still shows a hat-and-glasses icon when you go incognito, as if you're now in disguise.)
Incognito or private mode does indeed keep certain aspects of your browsing private, but it's important to be aware of what it hides and erases from your computer or phone and what it doesn't. Once you understand exactly what these modes do in your browser, you'll know when they can be most useful.
What Incognito Mode Does
Perhaps the easiest way to think about incognito mode is that as soon as you close the incognito window, your web browser forgets the session ever happened: Nothing is kept in your browsing history, and any cookies that have been created (those little bits of data that log some of your actions online) are promptly wiped.
Cookies are what keep items in your Amazon shopping cart even if you forget about them for days, for example, and they also help sites to remember if you've visited them before—which is why you normally only get pestered to sign up for a site's newsletter the first time you arrive. You might notice if you visit all your favorite sites in incognito mode, you won't get recognized, and are then asked to sign up for a whole load of newsletters and special offers all over again.
This sort of anonymity is what incognito mode is good at—it's like starting again with a blank slate, for better or for worse. Try loading up Twitter or Gmail, and these sites won't automatically log you in as they normally do. For the same reason, incognito mode can sometimes be a handy way of accessing more free articles from a paywalled site (the site won't instantly identify you as someone who's been before, although many paywalled sites use other methods to figure that out).
Your browser won't remember where you've been, what you've searched for, or the information you've filled into web forms while you've been in incognito mode—it's as if Chrome, Firefox, or whatever browser you're using has its back turned until you close down the incognito mode again.
With browsers now so personalized, you're probably familiar with your frequently visited websites appearing as you type into the address bar or search box. Anything you've visited or searched for while in incognito mode shouldn't appear in these suggestions (with a few caveats, as we'll mention below). You'll notice in some browsers that you can't pull the normal trick of reopening a tab you've just closed while in incognito mode—your browser has already forgotten that you ever opened it in the first place.
Incognito mode certainly has its uses: You can sign into multiple accounts at the same time, for instance, rather than signing in and out. It's also helpful when you need to run a few quick searches on sensitive topics—like health issues—that you don't want to show up in your browsing or search history in the future.
While all traces of your incognito activities will be gone as soon as you close these windows, this is true only as far as your browser and the device you're currently using are concerned. These days, tracking and data mining extends way beyond a single browser and a single device.
What Incognito Mode Doesn't Do
As soon as you log into any of your favorite sites in incognito mode—Facebook, Amazon, Gmail—your actions are no longer anonymous or temporary, at least as far as those services are concerned. Although cookies and tracking data are deleted when your private session finishes, they can still be used while the session is active, linking your activities between various accounts and profiles.
That means if you're signed into Facebook, for example, Facebook might well be able to see what you're up to on other sites and adjust its advertising accordingly, even in incognito mode. Blocking third-party cookies in your browser can stop this to some extent (Chrome even offers you the option when you open incognito mode), but such is the reach of ad networks and tracking technologies that it's difficult to stop it entirely.
Google has already been in trouble for this practice, though it's not alone. If you sign in to Google while using incognito mode, then your searches are once again being logged and associated with your account, assuming that's how your Google account preferences are set up—and Google is potentially also using its ad network and tracking technologies on other sites to keep tabs on you there too.
Even if you don't sign in anywhere, the websites that you visit can use various clues—your IP address, your device type, your browser—to figure out who you might be, and to tie this to other information that might already be associated with you. Certain browsers are fighting back against this type of tracking, called "fingerprinting," but it still goes on.
Incognito mode doesn't hide your browsing from your internet service provider or your employer, and it doesn't wipe out files you've downloaded. In other words, you need to think of it as a way of hiding your online activities from the particular browser on the particular device you're using, and from the other people using that device. When it comes to everything else, there are no guarantees.
The limits of incognito mode highlight just how hard it is to stay invisible on the web. To keep any tracking down to an absolute minimum, you need to pick a browser focused on privacy, use services like the DuckDuckGo search engine that don't mine your data, and deploy a reliable VPN program whenever you connect to the web. We've written more about the extra steps you can take here.