I know that you need a pin / password set up for the internet ID to work, but how likely is it that random hackers out there can guess what my internet ID is?
You are absolutely right as the knowledge of the Internet-ID code alone is not enough to be able to connect to a remote Host/Agent. It's necessary to know the Host's access credentials such as a password or a login/password pair depending on which authorization method is enabled on the remote Host. Of course, anyone can type random numbers in their Viewer and try connecting, but it simply would not lead them anywhere. However, you can always see the records about when a Host was accessed and in what connection mode, the connection entries can be found in the Host log files. In case if the connection was established you will see the entry that will state Access granted. In case if you use Agent, its connection logs are stored on the remote machine in the following folder: C:\Users\user_name\AppData\Roaming\Remote Utilities Agent\Logs\.
However, there are additional ways to protect your Host machines from any unauthorized access. For example, you can use Remote Utilities in a totally isolated environment (via Direct connection or RU Server) or enable 2-factor Authentication that provides an additional level of security and protects your Hosts from unauthorized access even if someone guessed or otherwise got possession of your access password. For more information on additional security measures please see our Security page.