Unknown devices on my Google account.

[Moonriver78]

7. I would like to know..

As well how they got on there because there are many, many people who have the same problem. Only thing I can think is that it had to have happened before you enabled two factor authentication. If you want you can go to a computer disable and then reenable two factor and that will sign out and kick all devices off and then you can reauthorize the ones you have in hand. You are secure at that point and if one tries to sign in again you will get a text. The recent activity page for google only shows active devices for the last 28 days. Sometimes if you do a google account checkup you can remove devices or even click them to see where they signed in from but if not they should eventually fall off your account as google cleans up old devices but that can take several months with no activity. Some programs and apps like Bluestacks and different emulators, desktop and mobile texting apps etc. can also spoof devices on your account and if you use them it looks like some strange phone has access when it is actually a program.