A Serial Number or Activation Key can be locked to prevent misuse.
If the Serial Number / Activation Key has not been used, you can add the key manually and lock it - see Administration / Setup, Add a Key on the Activation Server. Alternatively you can import a key list and lock the complete key list.
To prevent, that a key can be used again (even for an reinstallation on the same machine) you have to search for the key.
Select Data Management Tab, Transactions. In the field Entry Key type in the Serial Number and press Search. Then click on View to get the detail page of the record. Check: Is Locked and press Save.
If the option for regular online checks is used, the complete license is validated every x days. The next check will detect that the license is locked and lock the license on the local machine / server.
Select Data Management Tab, Transactions. In the field Entry Key type in the license identification. This could be the Serial Number or your own ID and press Search. Then click on View to get the detail page of the record. Check: Is Locked and press Save.