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How does Gmail detect when my mail is accessed from another computer? Does it keep track of my MAC address to check whether a new device is used? I think it doesn't have anything to do with IP address.

  • IP and location (country and city), Web Browser and device info. Also multiple failed login attempt is suspicious and google will notify the account owner. – Aiden Stewart Oct 28 '18 at 13:00
  • I tried logging in using a vpn, but it didn't notify me – child Oct 28 '18 at 14:05
  • Did you changed the device and browser too ? – Aiden Stewart Oct 28 '18 at 14:32
  • There is no way for the browser to determine your MAC address, based on stackoverflow.com/questions/3385/mac-addresses-in-javascript – multithr3at3d Oct 28 '18 at 15:16
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How does Gmail detect when my mail is accessed from another computer? Does it keep track of my MAC address to check whether a new device is used? I think it doesn't have anything to do with IP address.

You can test this by logging in with a different browser on the same computer and observing the account activity details (link is at the very bottom of your gmail front page.

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Detail should show a different browser at the same IP address.

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If you sign out of your gmail account, invalidating the session ID, and then log in again, you will not get a notice because the device is trusted, meaning google stores data used to fingerprint your computer and browser.
My other browser above was not known or trusted so I got a 2 factor prompt when tried to use it. Subsequent logins with that other browser did not get a notice / 2fa prompt because that browser is now trusted. If you look at the cookies in your browser, you see many google cookies that provide this trust.

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I cleared all google related cookies from my other browser and when I tried to login again, it did not recognize that browser as trusted.

If I walk down to the corner coffee shop or use a VPN, it will not look like a new device to google because the session cookie and the fingerprint data I mentioned above will be the same.
Google does not know your computer's mac address (Unless you are using google wifi).

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In general, web applications recognize not 'the computer', but 'the browser', as identified by browser cookies. To quote "Types of Cookies used by Google"

We use security cookies to authenticate users, prevent fraudulent use of login credentials, and protect user data from unauthorized parties.

That is why you will often get additional login security (2-factor or "security questions") if you log in from a different computer. You can test the same behavior by deleting your browser's cookies (caution: may be traumatic to the rest of your browsing) or using Incognito mode.

Most modern "know the client" technologies do not rely on IP address because it changes so often in this mobile world. The exception is that some applications will require extra authentication steps if the geolocation changes, e.g., you're suddenly trying to log in from an Eastern European ISP instead of one located in California.

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