Q: Guest User

Hey there ellenscub,

It sounds like you have concerns about the Guest User that you noticed after the last update. You can disable that in your System Preference:

Let occasional users log in as guests

 

A guest user account lets others use your Mac without setting up a full account or using someone else’s. You can use parental controls to limit guests’ activities, and specify which folders they can view.

1. In Users & Groups preferences, select Guest User in the list of accounts.
2. Select “Allow guests to log in to this computer.”
3. If you like, select “Enable parental controls,” then click Open Parental Controls. For details about the limits you can set, see:Set up parental controls
4. To let guests use your shared folders from another computer on the network, select “Allow guests to connect to shared folders.”

From: OS X Mavericks: Set up users on your Mac         

          http://support.apple.com/kb/PH14411?viewlocale=en_US

Here is some more information about what the Guest User is, and how it works on your computer:

OS X Mavericks: About users, administrators, groups, and guests

http://support.apple.com/kb/PH14180?viewlocale=en_US

Guest

To let others use your Mac temporarily and without adding them as users, set up a guest user. You can set restrictions on the guest user account so when a guest logs in to your Mac, they can access only the items you want to share. Guests don’t need a password to log in. While logged in, they can’t change user settings or computer settings. They also can’t log in remotely when remote login is turned on in Sharing preferences. Files created by a guest are stored in a temporary folder, but this folder and its contents are deleted when the guest logs out. The guest account works with the Find My Mac feature of iCloud. If someone finds your Mac and logs in as a guest, and then uses Safari to access the Internet, iCloud can detect this activity.

Thank you for using Apple Support Communities.

Regards,

Sterling