First things first: Your documents are NEVER available on the public internet after you upload them to PlagScan. As a single user, nobody has access to the full-text of your documents as long as you do not explicitly share your plagiarism reports. Here is a list of how your documents can serve as a source for others, based on their respective settings (again, WITHOUT sharing the full-text).

  Internet User database Organization database Plagiarism Prevention Pool
Compare with web sources never - - -
Check against my documents never + - -
Share with my organization never + + -
Become part of the Plagiarism Prevention Pool never + + +