ID and password are used to protect the system from unauthorized access.
However, if you want to have additional level of security, you can set Whitelist. Whitelist is a list of remote IDs which have the right to access your PC. All connection attempts from not-authorized computers will be blocked even if the correct password used.
In order to set or modify the Whitelist, select the item "Set Whitelist..." in the Settings menu:
Then enable the checkbox, and enter allowed IDs, one by one: