Using Public Computers Safely

Why a shared computer is different

At home, you know who uses your computer, what software is installed and when it was last updated. On a computer in a library, hotel lobby, print shop or school lab, you know none of that. The machine may be well managed, with automatic cleanup between users and current software. It may also be old, poorly maintained or, in rare cases, deliberately tampered with.

You usually cannot tell which of those you are looking at. So the sensible approach is not fear, but a simple rule: use a public computer for tasks where little is lost if something goes wrong, and keep your most sensitive activity for devices and networks you trust.

Decide what the task is worth

Before you sit down, think about what you actually need to do. A rough sorting helps.

• Low risk: looking up a bus timetable, reading a news article, checking a map, printing a public document.
• Medium risk: reading personal email, printing a boarding pass or ticket, using a social media account.
• High risk: banking, tax filing, entering card details, changing account passwords, accessing work systems or medical portals.

Low-risk tasks are generally fine. For medium-risk tasks, take extra care and follow the steps below. For high-risk tasks, wait if you can. For these, wait for a trusted connection or use mobile data instead.

Before you start

Take a few seconds to look at the machine and its surroundings.

• Look for anything odd. Unfamiliar devices plugged between the keyboard and the computer, loose cables or unexpected attachments are worth reporting to staff. Most machines are fine, but a quick glance costs nothing.
• Prefer a private browser window. A private window helps keep history and cookies from being saved on the machine afterward. Private browsing mode does not hide what you do from the network or the website, so treat it as cleanup help, not protection.
• Do not install anything. Do not add extensions, toolbars, plug-ins or programs. If a task needs software you cannot run without installing, it is probably not a task for this machine.
• Do not accept saved passwords. If the browser offers to remember a login or autofill a form, decline every time.

While you are using it

Be deliberate about what you type and open.

Type as little as possible. Every password, card number or answer you enter on an untrusted machine is something that could, in the worst case, be captured by software you cannot see. If you must sign in to an account, make sure it has two-step sign-in turned on, so that a stolen password alone is not enough. Approving the sign-in on your own phone is better than receiving a code you then type into the shared machine, since the code is only useful for a short time but a password is useful for much longer.

If you use a password manager on your phone, you can read a password from it, but typing it into a shared computer still exposes it. For a truly important account, it is better to postpone.

Watch the address bar. Confirm you are on the real site before signing in, because fake pages are as easy to run into on a shared machine as anywhere else. Habits such as checking for lookalike web addresses are the same here as at home.

Keep downloads to a minimum. If you must save a file, such as a document you need to print, avoid keeping anything personal on the computer. Where possible, use your own USB drive only if you are confident the machine is clean; otherwise email the file to yourself from a webmail account you then sign out of, or use a service you trust.

Finally, be aware of people nearby. Shoulder surfing and screen privacy matters in busy libraries and hotel lobbies: sit with your back to a wall if you can, and cover the keyboard while you type a password.

When you are finished

This is the step most people skip, and it is the one that matters most.

1. Sign out of every account you opened, using the site’s own sign-out button, not just closing the tab. Closing the browser does not always end a session.
2. Close the browser entirely, including any private windows.
3. Clear what you can. If you used a normal window, clear history, cookies and downloads for the session. If the system restarts or resets between users, that helps, but do not rely on it.
4. Delete files you saved, and empty the recycle bin or trash if the machine has one.
5. Check you have everything, including USB drives, printouts and any paper notes with passwords on them.

If you often use shared machines, it is worth making this routine second nature.

If you think you made a mistake

Suppose you realize you left an account signed in, or you typed a password on a machine that seemed suspicious. Do not panic, but act promptly from a device you trust.

• Change the password for that account, then for any other account that used the same one. Password reuse is what turns one exposed login into several.
• Review recent sign-in activity for unfamiliar devices or locations, and sign out of all other sessions if the service offers it.
• Watch for account takeover signs, such as password reset emails you did not request or messages sent from your account that you did not write.
• If the account is already misused, the guidance on hacked account response applies.

If you entered banking or card details, contact your bank or card issuer using the number on your card, and ask what they recommend. Outcomes vary, and early reporting generally gives you more options.

A reasonable mindset

Public computers exist so people can get things done when they lack their own device, and many people use them for years without any problem. The goal is not to avoid them, but to match the task to the risk. Keep your use brief, keep it simple, sign out every time, and save the important things for a device and connection you trust.