You should perform the following steps:
- Backup your database
- Log in with a known admin account
- Create a new admin account to use exclusively from this point on
- Delete all accounts with the exception of the one created in step 3.
- Delete any additional roles that were created
- If you had roles configured for a specific purpose, re-create them
- If you had users configured for a specific purpose, re-create them
Modules shouldn't be creating an admin accounts.
The only valid reason would be a specific need that you would have created them for. As the admin of your site, if you don't recognize something then delete it.
If you aren't comfortable deleting, then at the very least you should disable any accounts that you don't recognize, if they are legitimate the people you created them for will contact you saying they can't login.