Hi Phani
For me, this type of value usually means something has happened automatically. The types of activity that cause this could be:
- Upgrading from a previous version of CRM
- Having a workflow or Plugin run when a User is created, and the account it runs under is a System user
- Having users added to CRM by your Office 365 Administrator who uses a System account
- Perhaps moving data centres or hosting (not sure about this one...)
If you were On-Premises, it could also be caused by connecting a CRM database to CRM on a new server.
Unless you are concerned about an unauthorised CRM User being added, it isn't a great concern. Still, you may want to review the Security Roles of your users, just for peace of mind.
Good luck!
Brad Orders