No third party can just send, or push, something to you without you agreeing to it. Airdropping from a computer that are are signed into with your iCloud account to another computer, also signed in with the same iCloud account, can just transfer files without asking. Someone can Airdrop something to you, but you have to agree to it.This only is shared between computers that are signed in with the same iCloud account. Unless someone is using your computer without you knowing, it's probably not a security issue.In this case, it's a desktop, not a mobile device. The icon that you see there usually shows what device is 'handing off' from.
You can ignore it if you want, or select it to 'hand off' what you are doing on the other computer to this current one. An apps Handoff icon from iPhone near the right end of the Dock. (I'm assuming you have Chrome as your default browser) Some third-party apps may also work with Handoff. That computer has a window open in a web browser. For instance, if you open a Web page in Safari on a compatible iPhone, you might see a Safari icon at the left or top of your Dock.
Yes, the icon you see on the right is Handoff from another computer that you are signed into and are near. The Handoff section contains only a single icon and appears only if your Mac is receiving a Handoff signal from another iOS device or Mac.
