You cannot remove anything from another owner's MacBook; however, you can deny permission on your MacBook so that no other Mac can access any data from it.
Here are a few steps you need to take.
Step 1: Check Sharing Settings: Go to System Settings > General > Sharing and turn everything off, especially:
- File Sharing
- Screen Sharing
- Remote Login
- Remote Management
- Bluetooth Sharing
- Internet Sharing
Step 2: Forget All Wi-Fi Networks and Reset Network Settings
- Go to System Settings > Wi-Fi.
- Click the three dots (…) or Advanced (bottom right).
- Forget all unfamiliar networks.
- Reconnect only to your trusted home network.
Step 3: Check for Rogue Profiles and Configurations
Go to: System Settings > Privacy & Security > Profiles
If you see anything there that you didn’t install, delete it.
(If “Profiles” is missing, you’re clean in that regard.)
Step 4: Create a New Admin & Remove the Old One
If you think your current admin account is compromised:
- Go to System Settings > Users & Groups.
- Click the lock (bottom left), enter your password.
- Add a new Admin account.
- Log out and log in to the new one.
- Transfer files you trust, then delete the old user.
Step 5: Reset Your Router (Important)
If your internet is being blocked, your Wi-Fi router may have been tampered with.
- Hold the reset button (usually for 10 seconds).
- Reconfigure it using a strong password and WPA3 or WPA2 security.
- Change the Wi-Fi password and network name (SSID).
