In the past several years, most internet browsers have added a private browsing mode aimed at protecting user privacy. Chrome calls it Incognito Mode; it's Private Browsing in Opera, Safari, and Firefox.

Characterized by dark-color themes and icons of masked figures, these modes can give a user the impression they're browsing anonymously. Researchers at the University of Chicago and Leibniz University of Hannover found that many users think private browsing will protect them against malware, advertising, tracking scripts, and monitoring by internet service providers (ISPs).

Nothing could be further from the truth. Here's what private browsing does and doesn't do.

What Does Private Browsing Hide?

Cookies, those bits of data stored in the browser that enable websites to keep track of user information, let you stay logged into your online accounts when you open your browser. For some websites, cookies also keep track of settings you configure, such as language, layout, and themes.

Private browsing is designed to avoid keeping traces of your browsing session on your computer. So when you open a private window, cookies from your main browsing window aren't carried over. And when you close the private browsing window, all cookies you generated during your session will be destroyed.

In theory, without cookies, websites can't identify you. So opening a new private browsing window should make you appear to the internet as a new user.

In practice, however, websites can still discover your identity by correlating other information, such as your IP address, device types, and browsing habits (time of day, pages visited, and so on). Private browsing hides none of that data. Big tech companies such as Facebook and Google have plenty of information about users, and by connecting the dots, they can identify you, even if you haven't logged into your account.

After you close a private browsing window, your browsing history, saved passwords, and the content you type in text fields (usernames, phone numbers, and so on) for that window is wiped. This means that the next person who sits behind your computer and fires up the browser will not be able to find out which websites you visited during your private browsing session.

But if you bookmark a page when you're in private browsing mode, it will be added to the bookmarks of your normal browsing page and will be visible to everyone. Also note that files you download to your computer while privately browsing will not be deleted when you close the window.

Can Your ISP See What You Search in Incognito?

This is one area in which private browsing won't protect you at all. Your ISP, corporate network administrator, and government agencies will be able to track your browsing habits regardless of the browsing mode you're using.

As your gateway to the internet, ISPs and network administrators control your traffic at the network level and can keep track of the websites you visit whether you're in normal or private browsing mode. Many ISPs share this kind of information with advertising agencies, which will, in turn, use the data to target you with relevant ads.

To hide your internet traffic from surveillance and monitoring, you can use a virtual private network (VPN). VPNs encrypt internet traffic and channel it through a third-party server, which then directs it to the destination. Your ISP will know you're using a VPN, but it won't be able to figure out which websites you're visiting.

Although VPNs protect you against ISP snooping, they sometimes collect and sell your information to other parties. So for absolute privacy, use the Tor browser. Tor encrypts your traffic and bounces it across several computers, called Tor nodes, before reaching its destination. None of the Tor nodes have full information about the source and destination of your internet traffic and can't spy on you. Tor is more private than VPNs, but it's also slower.

Private Browsing Does Not Stop Malware, Viruses

In the aforementioned study by the University of Chicago and Leibniz University, 25 percent of respondents said they believe private browsing protects them against malware and malicious websites.

But most malware will cause harm after it is installed on your computer, and malicious websites will harm you regardless of your browsing mode. For instance, when you open a phishing email and download a malware-infected attachment while browsing in private mode, you won't be protected (by your browsing mode). Also, private browsing won't protect you against malware already installed on your computer: a keylogger, for example, that silently monitors your keystrokes and sends them to a hacker's server.

To protect yourself against malware, you'll need an antivirus.

An exception to this is malicious extensions—the third-party features you add to your browser. Some hackers hide malware in browser extensions and do things such as steal your credentials or mine cryptocurrencies. Edge, Chrome, and Opera disable extensions by default, which will protect you against malicious browser extensions that might have found their way to your browser. Other browsers won't disable extensions in private browsing, but it takes only a few clicks to do it manually, and it's considered a good privacy practice.

Private browsing is a very useful and handy tool for a quick surfing session that will not leave traces on your computer. With a few caveats, it will protect your privacy against other people who use your computer and reduce some of the information you reveal about yourself when visiting websites.

But private browsing won't make you anonymous and won't protect you against surveillance and big tech snooping. For that, you'll need true privacy tools.

Further Reading