As you browse the web, your web browser saves a lot of information about what you’re doing in order to improve your experience online. Here’s a list of some of the things that your web browser normally remembers:

• Cookies are stored so websites can recognize you automatically, making it possible to log in once instead of every time you load a new page.
• Some files from the sites you visit (like stylesheets, scripts, and images) are kept in a local cache so you don’t have to download them every time, making web browsing faster.
• The information you type into certain form fields is saved and made available the next time you fill out a similar form, saving you time.
• A list of the websites you visted is kept so you can find that one page you visited last Tuesday.

Most of the time, having your web browser store this stuff is useful and desirable but sometimes you might not want it to. That’s where private browsing comes in. In a private browsing session your web browser doesn’t keep a record of anything.

• No cookies or local storage entries are kept after your private browsing session ends.
• The browser cache is disabled.
• Autofill for forms and searches is turned off.
• Browsing history is not saved.

Private browsing mode is useful for several reasons. Some sites, like Google, will remember you (even if you don’t log in) and tailor content (like search results) based on your previous activity. If you want to see the raw, unaltered content you can use private browsing to make these sites “forget” about you temporarily.

Another handy use for private browsing is to log in with multiple accounts using the same web browser, or log out without actually logging out. This is possible because the temporary cookies and local storage kept for a private browsing session are totally isolated and separate from your normal cookies and local storage. Changing one has no effect on the other.

A Word of Warning

Now, all of that said, it’s important to understand what private browsing does not do. Just because your web browser isn’t keeping a record of your private browsing session doesn’t mean no information is being revealed or saved elsewhere.

• Your IP address is not concealed.
• Your network traffic is not hidden, meaning your ISP, employer, or even people on the same network can still see what you’re doing.
• The websites you visit can still see that someone is visiting them, and they may even be able to tell it’s specifically you using methods involving your IP address and other browsing data.
• Your browser may not disable browser extensions when in private browsing mode, and some of those extensions may be recording your browsing history.
• If your computer is infected with spyware or other malware, or you have monitoring software like a keylogger installed, that software can still keep track of your activity in a private browsing session.
• Other parts of your computer do keep some records, at a lower level, that can be used to reconstruct part or all of your private browsing history. This includes things like DNS cache entries, examining certain file time stamps, and more. Fairly technical stuff, but not impossible.

Remember, private browsing can be useful in a lot of situations, but it’s not magic. Now that you know how it works you can use it with confidence.