No one can guess the link — but if you post it publicly, anyone can see it.
By default your dashboard shares are private — the URLs aren't guessable, so only people you choose to share it with will see it.
However, anyone who sees it can themselves share it, so if you don't want your results shared, then only give it to people you trust. If a dashboard share gets posted publicly, it could get picked up by a search engine and listed.
If at any time you want to delete a dashboard share, you can do so easily with two clicks from the dashboard share page. This will immediately stop anyone (including yourself) from seeing the results.
If you can't find the answer to your question, or you have found a bug, have a suggestion or have feedback, please don't hesitate to contact us! Simply enter in your message below, or email us directly at firstname.lastname@example.org.