For a PC registered to your account, accounts other than yours can also ask to connect with the ID and that PC's device password. They get in only when someone at the PC allows it, and the connection request window shows that account's email as verified by the server. Your own account (the owner) still connects directly from My devices.
This chapter does not apply to unregistered PCs (PCs that take a one-time password).
When another account asks to connect, the connection request window shows:
Choose one of two for each PC.
A PC that runs only as a service without a window (a Linux server, for example) has no one to answer the prompt, so only emails on the trusted list get in and the rest are declined.
You can change the trusted list and the blocked list in two places; either way, it is the same list.
On the web: On the card in My devices, press Trusted emails (or n trusted). Enter an email and press Add, or use Remove and Unblock in the list. Below, under Requests from other emails, choose Ask in the prompt or Refuse at once.

In the host app: Do the same in the host window under Settings › Access rules.
For an account that keeps bothering you, use Block, or switch to Trusted emails only. Every attempt is kept, with the email, in the host window under Settings › Connection history.