But what does that really mean, and how well does private mode protect you from prying eyes—both client and server side? Let’s begin with a few definitions. First, searching the web in private mode simply means selecting a private window within your browser of choice. Depending on the browser, it goes by various names. For Microsoft Edge, you’d choose InPrivate and for Google Chrome you’d choose Incognito, and so on. We’ll get back to these and others in a bit. Secondly, let’s discuss client- and server-side threats. Client side refers to what happens on the device you are using. This includes everything from malware or keyloggers lurking on your machine to other users who share the same machine at work or at home, or especially in a public setting such as a library or internet café. It also encompasses browser activity such as tracking your history and caching pages for faster access on future visits. Server side refers to what happens on the other side of your connection, like webpages that use cookies to track your behavior or retarget you for marketing purposes. Next, let’s look at popular browsers to see what they do—and don’t do—to protect you while browsing in private mode.

Microsoft Edge InPrivate

Microsoft Edge Support states that using InPrivate tabs or windows means details of your online activity won’t be saved on your PC once you complete your search and close the window. This includes history, temporary internet files and cookies.

Google Chrome Incognito

Similarly to MS Edge, Incognito does not save your browsing history, cookies, site data or information you enter in forms. It does, however, keep any downloaded files or bookmarks created during the session. On websites you visit, your internet service provider can still see your activity, as can a school or employer who is providing your internet access or computer.

Firefox Private Browsing

Like Edge and Chrome, Firefox Private Browsing allows you to conduct your business online without it saving any information about the websites you visit, or which pages you looked at while there. Firefox adds additional Tracking protection to prevent others from collecting your activity across multiple sites. You can select specific third-party trackers to add to a block list.

Opera

Private browsing in Opera means that once you close a private tab, all of the data related to that tab are deleted including your browsing history, your cache, cookies and any logins you entered during the session. Further, the Opera Help site states, the tab cannot be recovered from “closed tabs,” but deliberately saved bookmarks will remain visible and accessible. Opera also offers a Do Not Track mode in its advanced security preferences, but it is not automatically turned on simply by opening a private tab. Opera Help also includes a section on how to delete private data for those times when you might have searched for a gift, for example, and realize after the fact that you don’t want the recipient to start receiving related ads, giving away your surprise. Deleting private data will also delete saved passwords and might mean resetting preferences on websites you’ve visited and want to keep, so be proactive and use a private tab before beginning your search.

Go completely private

Private mode or not, selecting a private window within a browser which routinely collects data unless otherwise asked to temporarily stop is not without risks. Edge’s InPrivate, in particular, has well-documented privacy-related bugs of which Microsoft notes it is aware, and working on fixing. Stay tuned. In the meantime, if you’re not willing to risk glitches, you might consider going completely private. Tor Browser is your doorway to the deep web, meaning it is not indexed and tracked the same way as the World Wide Web.

Tor has a security level high enough that it is the choice of many law enforcement and government agencies, along with the U.S. Navy. It doesn’t need to live on your computer, as it can be accessed from a thumb drive when needed. Once finished, simply eject the thumb drive and no trace will be left behind. Epic Browser isn’t as high-level as Tor, but it does disable DNS pre-fetching, doesn’t allow DNS caches, auto fills or third-party cookies. In addition to deleting data from its own memory, it also deletes cookies from Flash and Silverlight along with any associated database preferences or pepper data. SRWare Iron is similar to Google Chrome because they are both based on the open source Chromium project, but it doesn’t use a Unique User ID or search suggestions. More well-known options include DuckDuckGo, Yippy (optimized for kids by blocking adult content) and IXQuick, which does not record your IP address, browser or search history. If you are simply interested in avoiding being tracked by advertisers and don’t need the high security level of Tor, this would work just fine.