A password is always necessary to connect a device to a Dropbox account. If you see a device you don't recognize, it's possible you signed in to your Dropbox account on a new device and authorized it by mistake. It's possible that someone has access to your email and password account. This can happen if you ever shared your email and password with other people.
If you see a device you don't recognize, secure your Dropbox account by following these steps:
Dropbox logs the IP address of each device that accesses your account. You can use the IP address to discover the login location and the internet provider used.
You can use any IP address lookup service for more detailed information.
Note: The location information isn't always accurate. Some IP addresses might be associated with the wrong country. If the country isn't correct, you can check it using any online IP address lookup tool.
Note: The Dropbox folder is just a normal folder on your computer, so it's no more or less secure than every other folder on your computer. We recommend that you follow good security practices to protect your entire computer. This includes requiring a password to log in to your account, and to resume from sleep, screen savers and lock screens.