Below are a few possible reasons why a name you don't recognize might show up in your list of collaborators:
- You invited a mailing list, and an individual from the mailing list used the invitation to sign in to Google Docs and access your document or spreadsheet. In this case, although you didn't invite this person separately, this person was able to access by being on the invited mailing list.
- You invited a friend at one email address, but your friend used the invitation to sign in with another Google Account username and password. This can happen if the invitation was forwarded to an address different from the one originally used to invite your friend. In this case, you'll see this person listed twice, once with the address you used for the invite, and again with the different address that your friend used to sign in. The best way to determine if this is the issue is to contact the person at the address(es) listed.
- When you invited collaborators, you selected one of the following options: Collaborators may invite others, Editors can share this item, or Invitations may be used by anyone. If you selected the first or second option, your collaborators can invite others (whom you may or may not recognize) using the Share tab. If you selected the second option, your collaborators can't invite others using the Share tab, but they can pass along the invitation in email to allow others access.
- One of your invited collaborators changed the Display name associated with the person's Google Account. After switching display names, this person will appear to be new and unknown. If you suspect this is the case, send an email to make sure you can match the name to the collaborator.