What Does Private Browsing Mode Do?

Martin Shelton
6 min readJul 5, 2018
Opera’s private browsing mode

Most popular web browsers support two types of windows: ordinary windows and “private browsing” mode. Sometimes private browsing goes by a different name, such as InPrivate mode in Microsoft Edge, or Incognito mode in Google Chrome, but we’ll just call it private browsing. I research how people understand the web for a living. Trust me when I say, if you’re not sure what private browsing does, you’re in good company. Researchers have found widespread misconceptions about what information is visible through private browsing. So let’s talk about what it does and doesn’t do.

These windows and tabs all have one important thing in common: they don’t save your information in the browser after they’re closed.

Who sees what?

Let’s say you want to connect to Amazon.com. When you connect to a website, your computer is making a connection to another computer — or server — that hosts the website.

Much like you need a sending and receiving address to send and receive physical mail, your computer needs to know Amazon.com’s Internet Protocol address (or IP address) before it can connect. And websites need to see your IP so they know where to send the response.

A system works behind the scenes to tie domain names like Amazon.com to IP addresses, so we don’t have to think about it.

When you connect through someone else’s network, such as your workplace, the network administrator may see the traffic. Likewise, a bit like the mail carrier, the Internet Service Provider (or ISP, such as Comcast) needs to relay the connection request to websites you visit. For now, this means the ISP is able to read the sender and receiver as well. They may also hold onto, or share that information.

Some websites only allow for an unsecured connection (e.g., http://latimes.com), meaning the pages you visit can be seen by anyone in between you and the website you’re connecting to (such as the Internet Service Provider, or your network administrator).

For example, the “HTTP” in http://latimes.com means that you’re making an unsecured connection. But some websites allow you to make a secured HTTPS connection (e.g., https://amazon.com). The little lock icon in the address bar means that your connection to the website is secured with HTTPS, and the ISP can’t monitor the content on the page that you’re connecting to. This is awesome. However, they can still see that you’re visiting the domain, Amazon.com.

After you connect to a website, they can decide what to do with the information you gave them along the way. For example, they can make a log of the IP address you connected from. If you log into a website (e.g., Amazon) or share any information with that site after making a connection (e.g., looking at specific products) your activity may also be logged, just like outside of private browsing mode. They may also share that information with other groups, such as advertising partners.

What private browsing means

Safari’s private browsing prompt

Private browsing means the browser will forget some kinds of information only on your computer.

  • The browser won’t save a history of searches or websites you access on your computer.
  • The browser won’t save information, such as cookies or content from websites, that would ordinarily be saved onto your computer to help speed up future page loads.
  • Information entered in forms you fill out, such as credit card information, won’t be saved on the browser.
  • Generally, private browsing mode still allows you to save bookmarks and the files you download.

This can be useful for web searches you don’t want saved on your computer, and selectively fighting tracking. It’s a bit like telling your computer to forget everything you put into these tabs and windows, including the cookies and files that websites would ordinarily save locally. But it’s important to remember that connecting to the web means there are other groups involved too.

Private browsing doesn’t mean you are invisible

The private tab launch page on Mozilla Firefox

Be sure to read your private browsing windows closely, because they usually say what is and is not saved.

  • Even in private browsing, intermediaries such as your network administrator or ISP, and anyone they share your activity with, can still see your browsing activity.
  • Logging into a website means the website may still hold onto information about what you did there, and tie it to your other account activity outside of private browsing.
  • The websites you connect to can still see your IP address.
  • The websites you connect to can still see other identifying information embedded in the browser, such as the size of the window or the type of browser and operating system you’re connecting from.

Privacy networks

To learn more about preventing network snooping by your network administrator or ISP, consider looking into virtual private networks, which create a secured tunnel through a remote server before connecting to the web. However, know that a virtual private network can see anything your ISP can, and the websites you connect to can still see you just fine. It does not make you anonymous.

To learn more about browsing more anonymously, consider investigating Tor Browser, an easy-to-use browser built on top of Mozilla Firefox. Tor is now offered in the Brave browser, too.

Tor secures and bounces your connection around the world in its network before connecting you to websites, allowing you to appear to come from another location. For example, if you connect to Twitter in Tor Browser, you may appear to come from another country.

Tor isn’t perfect, so look into whether it’s right for you. Because your connection is taking extra laps around the world, it can be slower than a regular web connection. In rare circumstances, Tor may not be confidential. Likewise, your ISP can’t see what you’re doing within Tor, but they can still tell you’re using it. It’s also important to note that if you log into a personal account (e.g., Twitter) within Tor Browser, the company now knows who you are.

Private browsing mode can be useful for some situations — for automatically shutting down search history so your roommate can’t read it later, or temporarily fighting tracking cookies on the web so advertisers have a tougher time seeing what shoes you want to buy. Depending on your needs, we may want other tools to prevent network snooping, or to let you browse the web more anonymously.

Safe travels!

Last updated September 10, 2018.



Martin Shelton

Writing about security for journalists, as well as beginners. Principal researcher at @freedomofpress. freedom.press/training