Puppy Linux typically is a single user OS. The single user is run as the root account with full privileges. This is equivalent to being the administrator in Windows. That is there is no file a user can't modify (unless its read only) and no command that is prohibited.

It has been argued that running as root is not significantly less secure that running with other user accounts with less privileges.

Some Puppy versions also come with spot and/or fido accounts that don't have root privileges. They can be used to run browser and other networking software to add an extra level of security.

MultiUser - Puppy versions set up for more than one user

AttackPup - Puppy for network testing

PenetrationTesting penetration testing - network testing

Privacy - Keeping your information private

WatchDog - Puppy for securing your home

Fido on Barry's blog

How to use Spot restricted user thread

Security in Puppy Linux: running as Root thread

Running as Root - tallboy's post

Puppy GROWL thread

Lobster security podcast