What actually stays behind on a public computer
2026-09-25
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You are on the bus home and it lands on you. The hotel business centre. You checked your email, printed the boarding pass, and walked out. You do not remember signing out.
The first reaction is usually a vague dread that everything you did is now sitting on that machine for anyone to find. That is not quite true. Some things stay, some things do not, and a few of the things that stay can be dealt with from your phone in about five minutes. It helps to know which is which.
What stays
The signed-in session. This is the one that matters most. Closing the browser window does not sign you out. Most sites keep you logged in with a cookie that lasts days or weeks, so the next person to open that browser and visit the same site may land straight in your account. This is the thing to fix first.
A saved password. If the browser offered to remember your password and you clicked yes, or clicked anything in a hurry, it is now saved in that browser's password manager. The next person may not see it directly, but the login form will fill itself in.
Form autofill. Separate from passwords. Your email address, name, phone number and anything else you typed into a form can be remembered and offered to the next person who clicks into a similar field. Less dangerous than a password, more personal than people expect.
History and address bar suggestions. Every page you visited, and the address bar will suggest them to the next person who types the first few letters. Usually harmless on its own. Occasionally revealing, if the address itself contained something like a reset link or a document name.
Downloads. The boarding pass PDF you opened is very likely in the Downloads folder. Browser private modes do not change this. Files you downloaded stay on the disk after the private window closes, because they are no longer the browser's to forget.
A trusted device. If signing in triggered two-factor and you ticked the box to trust this browser, that machine may be able to sign in without a second factor for a while.
The clipboard. Whatever you last copied is still there until something else replaces it or the machine restarts.
What mostly does not stay
If you used a private or incognito window, history, cookies and form data from that window are discarded when the last private window is closed. That covers the session problem, as long as every private window was actually closed.
Many library and café machines also reset themselves between users or overnight. You cannot rely on it, but it does mean the odds are often better than your stomach suggests.
What to do from your phone, right now
Start with the session, because it is the one someone could use immediately.
- Google: open your Google Account, go to Security, then Your devices. Find the unfamiliar Windows or Mac entry and sign it out.
- Microsoft: the security section of your Microsoft account has an option to sign out everywhere. It can take a while to apply across every service.
- Facebook and Instagram: the "Where you're logged in" list in settings lets you end any single session.
- Anything else: look for a page called devices, sessions or security activity. Most large services have one now.
Then change the password if there is any chance it was saved or seen. On many services, changing the password also ends other active sessions, which makes it a useful second step even when you did find the right sign-out button.
Finally, if the service has a list of trusted devices for two-factor, remove the one you do not recognise.
You cannot clear that machine's history or Downloads folder remotely. If there was something sensitive in the download, the practical options are to call the front desk and ask them to clear the computer, or accept it and change whatever that document gives access to.
Removing the step you forgot
Every item in the first list, apart from the clipboard and the download, starts with signing in. The most reliable way to avoid this bus ride is to not sign in on a shared machine at all when all you need is a piece of text on its screen. We wrote about the practical routine for that in the library computer post.
Our own service exists for that narrow case. ZAGO.TO gives you four digits for text on your phone, and you type them on the public computer. Nothing to sign into, so nothing to sign out of later.
It does not make the machine clean, and it would be wrong to claim it does. The address is in the history. The text appeared on that screen, and if someone was standing behind you, they saw it. If you copied it, it sits in that clipboard. The text is on our server, readable by us, for up to two minutes, and after that you cannot open it again. It carries text only, not the PDF. What changes is the list of things you have to remember on the way out, which becomes much shorter than the one above.