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Practical Mac

Every time we use a browser, we leave behind extensive traces of ourselves. On a home computer shared by others, this can vary from the innocuous, such as searching for a birthday gift; to the embarrassing, when browsing a few dozen pages of the latest swimsuit issue of a leading sports magazine; to the actually secret, like researching whether an aging relative who may be in the same home has dementia. (All hypothetical situations, of course.)

It’s also the case that if you use a computer or mobile device that belongs to a friend, colleague, stranger or public library, you likely don’t want to leave details of what you viewed, or browser cookies that might allow another party to log in to an accidentally stored account. Some popular websites retain a logged-in state for minutes or months on a computer that doesn’t change its Internet address. (, banks and other financial and e-commerce sites typically don’t keep sessions active without prompting, and either log out the browser automatically after a preset period or require a visitor to re-enter a password to make a purchase or view accounts.)

Most browsers, nearly from their first releases, let you delete the contents of temporarily stored data (“purge the cache,” as it’s called); private browsing sessions are more recent and have changed a bit over time.

Many people I’ve spoken to either are unaware that such options exist or assume “private” always means looking at photos of unclad people rather than more general protection against leaving data available for others’ use or perusal. Whatever the issue, erasing a browsing session is easy to do.

Let’s look at popular Mac OS X browsers and iOS browsers.

Safari in Mac OS X: To dump stored data, select Safari > Reset Safari. The browser offers a dialog box that allows emptying caches, deleting cookies (tokens stored by websites in the browser’s database), removing stored passwords and form values, and resetting all the warnings that it offers against unsafe behavior. Check or uncheck boxes as you wish, and click Reset.

Safari > Private Browsing enables a mode that disables keeping track of where you go and, when the mode is disabled (by selecting the menu item again) dumps any values stored in the session. A “PRIVATE” label in the Location bar at far right reminds you the mode is active.

Firefox in Mac OS X: Tools > Clear Recent History offers similar options to Safari with clearer labels. You can dump the cache (stored pages), cookies, form values and other options, but also pick from the Time Range to Clear menu for how far back to remove data. Click Clear Now to execute the choices.

Tools > Start Private Browsing closes all current tabs and opens a new one with an explanation of what won’t be recorded in this mode. The phrase “(Private Browsing)” appears in the title bar. Select the same menu item again and privately viewed tabs are closed and the previous session’s tabs restored.

Chrome in Mac OS X. Chrome > Clear Browsing Data is similar to Firefox’s in options and in picking a range. Click Clear Browsing Data to dump the selected options.

Google calls Chrome’s private mode “Incognito,” and it’s enabled by selecting New > New Incognito Window. Everything in that window, which has a dark background at the top and the outline of a fedora-hatted spy at its upper right, is kept private. Closing the window dumps all cookies, search history and other data used in the session.

Safari in iOS: Launch the Settings app and slide down to the Safari icon and tap it. You can remove the list of recent pages by tapping Clear History, or tap Clear Cookies and Data to purge everything else.

Tap the On/Off button next to Private Browsing, and you’re prompted for whether you want to keep current tabs open when private browsing is enabled. Tap to turn it off, and you’re prompted again for whether to keep private tabs open when all the other data is dumped. Private browsing in Safari is indicated by a darker color around the fields at the app’s top.

Chrome in iOS: Tap the three-horizontal-line button and tap Settings, then tap Privacy. You then have the option to clear browsing history, the cache, cookies and data stored by websites on your iOS device, or everything (Clear All). You can also dump passwords stored in the browser. To create an Incognito session, tap the three-line button and then New Incognito Tab.

Removing data and going undercover doesn’t solve all security problems, but it’s a smart way to avoid leaving data behind when you intend to sweep the screen clean.